Corvus Pharmaceuticals (CRVS) 10-K 9 Mar 20 2019 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Mar. 09, 2020	Jun. 30, 2019
Document And Entity Information
Document Type	10-K
Document Period End Date	Dec. 31, 2019
Entity Registrant Name	Corvus Pharmaceuticals, Inc.
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Shell Company	false
Entity Public Float			$ 65.7
Entity Common Stock, Shares Outstanding		29,326,900
Entity Central Index Key	0001626971
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Amendment Flag	false

BALANCE SHEETS

BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 5,154	$ 39,196
Marketable securities	72,828	75,401
Prepaid and other current assets	1,362	992
Total current assets	79,344	115,589
Property and equipment, net	1,462	2,180
Operating lease right-of-use asset	2,327	0
Other assets	513	463
Total assets	83,646	118,232
Current liabilities:
Accounts payable	2,448	1,998
Operating lease liability	878
Accrued and other liabilities	6,899	5,029
Total current liabilities	10,225	7,027
Operating lease liability	2,310
Other liabilities		869
Total liabilities	12,535	7,896
Commitments and contingencies (Note 12)
Stockholders' equity:
Preferred stock: $0.0001 par value; 10,000,000 shares authorized at December 31, 2019 and December 31, 2018; 0 shares issued and outstanding at December 31, 2019 and December 31, 2018
Common stock: $0.0001 par value; 290,000,000 shares authorized at December 31, 2019 and December 31, 2018; 27,953,233 and 29,323,930 shares issued and outstanding at December 31, 2019 and December 31, 2018, respectively	3	3
Additional paid-in capital	288,224	280,840
Accumulated other comprehensive income (loss)	29	(34)
Accumulated deficit	(217,145)	(170,473)
Total stockholders' equity	71,111	110,336
Total liabilities and stockholders' equity	$ 83,646	$ 118,232

BALANCE SHEETS (Parenthetical)

BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2019	Dec. 31, 2018
BALANCE SHEETS
Preferred stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized	290,000,000	290,000,000
Common stock, shares issued	27,953,233	29,323,930
Common stock, shares outstanding	27,953,233	29,323,930

STATEMENTS OF OPERATIONS AND CO

STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating expenses:
Research and development	$ 37,975	$ 38,586	$ 46,305
General and administrative	10,879	10,636	10,219
Total operating expenses	48,854	49,222	56,524
Loss from operations	(48,854)	(49,222)	(56,524)
Interest income and other expense, net	2,182	2,283	861
Net loss	$ (46,672)	$ (46,939)	$ (55,663)
Net loss per share, basic and diluted (in dollars per share)	$ (1.59)	$ (1.71)	$ (2.72)
Shares used to compute net loss per share, basic and diluted (in shares)	29,349,810	27,509,960	20,488,506
Other comprehensive loss:
Unrealized gain (loss) on marketable securities	$ 63	$ 7	$ (2)
Comprehensive loss	$ (46,609)	$ (46,932)	$ (55,665)

STATEMENTS OF CHANGES IN STOCKH

STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Follow On Public OfferingCommon Stock.	Follow On Public OfferingAdditional Paid-In Capital	Follow On Public Offering	At-the-market offeringCommon Stock.	At-the-market offeringAdditional Paid-In Capital	At-the-market offering	Common Stock.	Additional Paid-In Capital	Accumulated Other Comprehensive Income	Accumulated Deficit	Total
Balance at Dec. 31, 2016							$ 2
Balance at Dec. 31, 2016								$ 200,709	$ (39)	$ (67,871)	$ 132,801
Balance (in shares) at Dec. 31, 2016							20,922,428
Increase (Decrease) in Stockholders' Deficit
Issuance of common stock					$ 711	$ 711
Issuance of stock (in shares)				52,569
Common stock issued on exercise of stock options								731			731
Common stock issued on exercise of stock options (in shares)							66,253
Vesting of restricted stocks issued upon early exercise of stock options								28			28
Stock-based compensation expense								6,229			6,229
Unrealized gain (loss) on marketable securities									(2)		(2)
Net loss										(55,663)	(55,663)
Balance at Dec. 31, 2017							$ 2	208,408	(41)	(123,534)	84,835
Balance (in shares) at Dec. 31, 2017							21,041,250
Increase (Decrease) in Stockholders' Deficit
Issuance of common stock	$ 1	$ 64,876	$ 64,877
Issuance of stock (in shares)	8,117,647
Common stock issued on exercise of stock options								393			393
Common stock issued on exercise of stock options (in shares)							165,033
Vesting of restricted stocks issued upon early exercise of stock options								28			28
Stock-based compensation expense								7,135			7,135
Unrealized gain (loss) on marketable securities									7		7
Net loss										(46,939)	(46,939)
Balance at Dec. 31, 2018							$ 3	280,840	(34)	(170,473)	110,336
Balance (in shares) at Dec. 31, 2018							29,323,930
Increase (Decrease) in Stockholders' Deficit
Retirement of common stock in exchange for common stock warrant								(5,030)			(5,030)
Retirement of common stock in exchange for common stock warrant (in shares)							(1,458,000)
Issuance of common stock warrant in exchange for retirement of common stock								5,030			5,030
Common stock issued on exercise of stock options								24			24
Common stock issued on exercise of stock options (in shares)							87,303
Vesting of restricted stocks issued upon early exercise of stock options								12			12
Stock-based compensation expense								7,348			7,348
Unrealized gain (loss) on marketable securities									63		63
Net loss										(46,672)	(46,672)
Balance at Dec. 31, 2019							$ 3	$ 288,224	$ 29	$ (217,145)	$ 71,111
Balance (in shares) at Dec. 31, 2019							27,953,233

STATEMENTS OF CASH FLOWS

STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash flows from operating activities
Net loss	$ (46,672)	$ (46,939)	$ (55,663)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	743	847	842
Accretion related to marketable securities	(644)	(608)	(195)
Stock-based compensation	7,348	7,135	6,229
Changes in operating assets and liabilities:
Prepaid and other current assets	(370)	187	(44)
Operating lease right-of-use asset	599
Other assets	(50)	406
Accounts payable	450	(1,456)	1,554
Accrued and other liabilities	2,030	(458)	1,499
Operating lease liability	(767)
Other long-term liabilities	12	(102)	(434)
Net cash used in operating activities	(37,321)	(40,988)	(46,212)
Cash flows from investing activities
Purchases of marketable securities	(138,586)	(161,861)	(88,309)
Maturities of marketable securities	141,866	132,024	173,401
Purchases of property and equipment	(25)	(355)	(266)
Net cash provided by (used in) investing activities	3,255	(30,192)	84,826
Cash flows from financing activities
Proceeds from issuance of common stock, net (includes $30,850 in aggregate gross proceeds from related parties for the year ended December 31, 2018)		64,877	711
Proceeds from exercise of common stock options	24	393	731
Net cash provided by financing activities	24	65,270	1,442
Net decrease in cash and cash equivalents	(34,042)	(5,910)	40,056
Cash and cash equivalents at beginning of the period	39,196	45,106	5,050
Cash and cash equivalents at end of the period	$ 5,154	39,196	$ 45,106
Supplemental disclosures of cash flow information
Purchases of property and equipment incurred but not paid		$ 84

STATEMENTS OF CASH FLOW (Parent

STATEMENTS OF CASH FLOW (Parenthetical) $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)
STATEMENTS OF CASH FLOWS
Proceeds from issuance of common stock, net, from related parties	$ 30,850

Organization

Organization	12 Months Ended
	Dec. 31, 2019
Organization
Organization	1. Organization Corvus Pharmaceuticals, Inc. (“Corvus” or the “Company”) was incorporated in Delaware on January 27, 2014 and commenced operations in November 2014. Corvus is a clinical stage biopharmaceutical company focused on the development and commercialization of precisely targeted oncology therapies. The Company’s operations are located in Burlingame, California. Initial Public Offering On March 22, 2016, the Company’s registration statement on Form S-1 (File No. 333-208850) relating to its initial public offering (“IPO”) of its common stock was declared effective by the Securities and Exchange Commission (“SEC”) and the shares of its common stock began trading on the Nasdaq Global Market on March 23, 2016. The public offering price of the shares sold in the IPO was $15.00 per share. The IPO closed on March 29, 2016, pursuant to which the Company sold 4,700,000 shares of its common stock. On April 26, 2016, the Company sold an additional 502,618 shares of its common stock to the underwriters upon partial exercise of their over-allotment option, at the initial offering price of $15.00 per share. The Company received aggregate net proceeds of approximately $70.6 million, after underwriting discounts, commissions and offering expenses. Immediately prior to the consummation of the IPO, all outstanding shares of convertible preferred stock were converted into common stock. Follow-on Public Offering In March 2018, the Company completed a follow-on public offering in which the Company sold 8,117,647 shares of common stock at a price of $8.50 per share, which included 1,058,823 shares issued pursuant to the underwriters’ exercise of their option to purchase additional shares of common stock. The aggregate net proceeds received by the Company from the offering were approximately $64.9 million, net of underwriting discounts and commissions and offering expenses payable by the Company. Liquidity The Company is subject to risks and uncertainties common to early-stage companies in the biotechnology industry, including, but not limited to, development by competitors of new technological innovations, protection of proprietary technology, dependence on key personnel, contract manufacturer and contract research organizations, compliance with government regulations and the need to obtain additional financing to fund operations. Since commencing operations in 2014, the majority of the Company’s efforts have been focused on the research and development of ciforadenant, CPI-006 and CPI-818. The Company believes that it will continue to expend substantial resources for the foreseeable future as it continues clinical development of, seek regulatory approval for and, if approved, prepare for the commercialization of ciforadenant, CPI-006, and CPI-818, as well as product candidates under the Company’s other development programs. These expenditures will include costs associated with research and development, conducting preclinical studies and clinical trials, obtaining regulatory approvals, manufacturing and supply, sales and marketing and general operations. In addition, other unanticipated costs may arise. Because the outcome of any clinical trial and/or regulatory approval process is highly uncertain, the Company may not be able to accurately estimate the actual amounts necessary to successfully complete the development, regulatory approval process and commercialization of ciforadenant, CPI-006, CPI-818 or any other product candidates. The Company does not expect its existing capital resources to be sufficient to enable it to fund the completion of its clinical trials and remaining development program of ciforadenant, CPI-006 or CPI-818 through commercialization. In addition, its operating plan may change as a result of many factors, including those described in this Annual Report on Form 10-K for the year ended December 31, 2019. The Company has incurred significant losses and negative cash flows from operations in all periods since inception and had an accumulated deficit of $217.1 million as of December 31, 2019. The Company has historically financed its operations primarily through the sale of redeemable convertible preferred stock and common stock. While the Company has been able to raise multiple rounds of financing, there can be no assurance that in the event the Company requires additional financing, such financing will be available on terms which are favorable or at all. Failure to generate sufficient cash flows from operations, raise additional capital or reduce certain discretionary spending would have a material adverse effect on the Company’s ability to achieve its intended business objectives. As of December 31, 2019, the Company had cash, cash equivalents and short-term marketable securities of $78.0 million. Management believes that the Company’s current cash, cash equivalents and short-term marketable securities will be sufficient to fund its planned operations for at least 12 months from the date of the issuance of these financial statements Exchange Warrants On November 8, 2019, the Company entered into an exchange agreement (the “Exchange Agreement”) with an Investor and its affiliates (the “Exchanging Stockholders”), pursuant to which the Company exchanged an aggregate of 1,458,000 shares of the Company’s common stock, par value $0.0001 per share, owned by the Exchanging Stockholders for pre-funded warrants (the “Exchange Warrants”) to purchase an aggregate of 1,458,000 shares of common stock (subject to adjustment in the event of any stock dividends and splits, reverse stock split, recapitalization, reorganization or similar transaction, as described in the Exchange Warrants), with an exercise price of $0.0001 per share. The Exchange Warrants will expire ten years from the date of issuance. The Exchange Warrants are exercisable at any time prior to expiration except that the Exchange Warrants cannot be exercised by the Exchanging Stockholders if, after giving effect thereto, the Exchanging Stockholders would beneficially own more than 9.99% of the Company’s common stock, subject to certain exceptions. In accordance with Accounting Standards Codification Topic 505, Equity, and Accounting Research Bulletin 43, the Company recorded the retirement of the common stock exchanged as a reduction of common shares outstanding and elected to record the excess over par value as a debit to additional paid-in-capital at the fair value of the Exchange Warrants on the issuance date. The Exchange Warrants are classified as equity in accordance with Accounting Standards Codification Topic 480, Distinguishing Liabilities from Equity, and Accounting Standards Codification Topic 815, Derivatives and Hedging, and the fair value of the Exchange Warrants was recorded as a credit to additional paid-in capital and is not subject to remeasurement. The Company determined that the fair value of the Exchange Warrants is substantially similar to the fair value of the retired shares on the issuance date due to the negligible exercise price for the Exchange Warrants. As of December 31, 2019, none of the Exchange Warrants have been exercised.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2019
Summary of Significant Accounting Policies
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation The accompanying financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“U.S. GAAP”). The Company’s functional and reporting currency is the U.S. dollar. The accompanying financial statements have been prepared on a going-concern basis, which contemplates the realization of assets and discharge of liabilities in the normal course of business. Since its inception, the Company has incurred significant losses and negative cash flows from operations. As of December 31, 2019, the Company had an accumulated deficit of $217.1 million and cash, cash equivalents and marketable securities of $78.0 million. The Company has financed its operations primarily with the proceeds from the sale of stock. The Company will need to raise additional capital to meet its business objectives. The Company believes that its current cash, cash equivalents and marketable securities will be sufficient to fund its planned expenditures and meet its obligations through at least the next twelve months from the issuance of these financial statements. Use of Estimates The preparation of the Company’s financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. Actual results could differ from such estimates. Concentrations of Credit Risk and Other Risks and Uncertainties Substantially all of the Company’s cash and cash equivalents are deposited in accounts with two financial institutions that management believes are of high credit quality. Such deposits may, at times, exceed federally insured limits. The Company maintains its cash with an accredited financial institution and accordingly, such funds are subject to minimal credit risk. The Company’s marketable securities consist of investments in U.S. Treasury securities, U.S. government agency securities and corporate debt obligations, which can be subject to certain credit risks. However, the Company mitigates the risks by investing in high-grade instruments, limiting its exposure to any one issuer, and monitoring the ongoing creditworthiness of the financial institutions and issuers. The Company has not experienced any losses on its deposits of cash, cash equivalents or marketable securities. The Company is subject to a number of risks similar to other early stage biopharmaceutical companies, including, but not limited to, the need to obtain adequate additional funding, possible failure of preclinical testing or clinical trials, its reliance on third parties to conduct its clinical trials, the need to obtain marketing approval for its product candidates, competitors developing new technological innovations, the need to successfully commercialize and gain market acceptance of the Company’s product candidates, its right to develop and commercialize its product candidates pursuant to the terms and conditions of the licenses granted to the Company, and protection of proprietary technology. If the Company does not successfully commercialize or partner any of its product candidates, it will be unable to generate product revenue or achieve profitability. Segments Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision‑maker in making decisions regarding resource allocation and assessing performance. The Company views its operations and manages its business in one operating segment, that of the development of and commercialization of precisely targeted oncology therapies. Cash, Cash Equivalents and Marketable Securities The Company considers all highly liquid investment securities with remaining maturities at the date of purchase of three months or less to be cash equivalents. Investments with remaining maturities, at the date of purchase, greater than three months are classified as “available-for-sale” and are carried at fair value with unrealized gains and losses, if any, included as a component of accumulated other comprehensive income (loss) in stockholders’ equity. Interest and realized gains and losses are included in interest income. Realized gains and losses are recognized based on the specific identification model. Fair Value Measurements Fair value accounting is applied for all financial assets and liabilities and non-financial assets and liabilities that are recognized or disclosed at fair value in the financial statements on a recurring basis (at least annually). The carrying amount of the Company’s financial instruments, including cash equivalents, accounts payable and accrued liabilities, approximate fair value due to their short-term maturities. Property and Equipment, Net Property and equipment are stated at cost and depreciated using the straight‑line method over the estimated useful lives of the respective assets: Laboratory equipment years Computer equipment and purchased software years Leasehold improvements Shorter of asset's useful life or remaining term of lease Maintenance and repairs that do not extend the life or improve the asset are expensed when incurred. When assets are retired or otherwise disposed of, the cost and accumulated depreciation or amortization are removed from the balance sheet and any resulting gain or loss is reflected in operations. Impairment of Long‑Lived Assets The Company regularly reviews the carrying value and estimated lives of all of its long-lived assets, including property and equipment, to determine whether indicators of impairment may exist which warrant adjustments to carrying values or estimated useful lives. The determinants used for this evaluation include management’s estimate of the asset’s ability to generate positive income from operations and positive cash flow in future periods as well as the strategic significance of the assets to the Company’s business objectives. Should impairment exist, the impairment loss to be recognized is measured by the amount by which the carrying amount of the asset exceeds the projected discounted future net cash flows arising from the asset. All long-lived assets are maintained in the United States of America. Research and Development Expenses The Company records research and development expenses as incurred. The Company accounts for nonrefundable advance payments for goods and services that will be used in future research and development activities as expenses when the goods have been received or when the service has been performed rather than when the payment is made. Research and development expenses consist of costs incurred by the Company for the discovery and development of the Company’s product candidates and include: · employee‑related expenses, including salaries, benefits, travel and non‑cash stock‑based compensation expense; · external research and development expenses incurred under arrangements with third parties, such as contract research organizations, contract manufacturing organizations, academic and non‑profit institutions and consultants; · costs to acquire technologies to be used in research and development that have not reached technological feasibility and have no alternative future use; · license fees; and · other expenses, which include direct and allocated expenses for laboratory, facilities and other costs. Clinical Trial Accruals Costs for preclinical studies and clinical trial activities are recognized based on an evaluation of the vendors’ progress towards completion of specific tasks, using data such as clinical site activations, patient enrollment or information provided to the Company by its vendors regarding their actual costs incurred. Payments for these activities are based on the terms of individual contracts and payment timing may differ significantly from the period in which the services are performed. The Company determines accrual estimates through reports from and discussions with applicable personnel and outside service providers as to the progress or state of completion, or the services completed. The Company’s estimates of accrued expenses as of each balance sheet date are based on the facts and circumstances known at the time. Stock‑Based Compensation The Company maintains incentive plans under which incentive stock options and nonqualified stock options may be granted to employees and non‑employee service providers. The Company accounts for stock-based employee compensation arrangements in accordance with the provisions of ASC 718, “Compensation—Stock Compensation.” For stock options granted to employees, the Company recognizes compensation expense for all stock-based awards based on the grant-date estimated fair values. The value of the award is recognized as an expense ratably over the requisite service period. The fair value of stock options is determined using the Black-Scholes option pricing model. Forfeitures are accounted for when they occur. Stock-based compensation expense related to stock options granted to non-employees is recognized based on the fair value of the stock options, determined using the Black-Scholes option pricing model. The awards generally vest over the time period the Company expects to receive service from the non-employee. Income Taxes The Company accounts for income taxes under the asset and liability method. The Company estimates actual current tax exposure together with assessing temporary differences resulting from differences in accounting for reporting purposes and tax purposes for certain items, such as accruals and allowances not currently deductible for tax purposes. These temporary differences result in deferred tax assets and liabilities, which are included in the Company’s balance sheets. In general, deferred tax assets represent future tax benefits to be received when certain expenses previously recognized in the Company’s statements of operations and comprehensive loss become deductible expenses, under applicable income tax laws or when net operating loss or credit carryforwards are utilized. Accordingly, realization of the Company’s deferred tax assets is dependent on future taxable income against which these deductions, losses and credits can be utilized. The Company must assess the likelihood that the Company’s deferred tax assets will be recovered from future taxable income and a valuation allowance is recorded when it is more likely than not that the deferred tax asset will not be recovered. The Company applies judgment in the determination of the financial statement recognition and measurement of a tax position taken or expected to be taken in a tax return. Based on the available evidence, the Company is unable, at this time, to support the determination that it is more likely than not that its deferred tax assets will be utilized in the future. Accordingly, the Company recorded a full valuation allowance for all periods presented. The Company intends to maintain a valuation allowance until sufficient evidence exists to support its reversal. The Company recognizes benefits of uncertain tax positions if it is more likely than not such positions will be sustained upon examination based solely on their technical merits as the largest amount of benefit that is more likely than not to be realized upon the ultimate settlement. The Company recognizes any material interest and penalties related to unrecognized tax benefits in income tax expense. The Company is required to file income tax returns in the U.S. federal jurisdiction. The Company currently is not under examination by the Internal Revenue Service or other jurisdictions for any tax years. Comprehensive Loss Comprehensive loss includes net loss as well as other changes in stockholders’ equity that result from transactions and economic events other than those with stockholders. The Company’s only element of other comprehensive loss in any period presented was unrealized gains and losses on available-for-sale marketable securities. Net Loss per Share Basic net loss per share is calculated by dividing the net loss by the weighted average number of common shares outstanding and Exchange Warrants outstanding during the period, without consideration of potentially dilutive securities. In accordance with Accounting Standards Codification Topic 260, Earnings Per Share , the Exchange Warrants are included in the computation of basic net loss per share because the exercise price is negligible and they are fully vested and exercisable at any time after the original issuance date. Diluted net loss per share is computed by dividing the net loss by the weighted average number of common shares, Exchange Warrants, and potentially dilutive securities outstanding for the period. Diluted net loss per share is the same as basic net loss per share for all periods presented since the effect of potentially dilutive securities is anti-dilutive given the net loss of the Company. Recent Accounting Pronouncements In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2014-09, Revenue from Contracts with Customers, which required an entity to recognize the amount of revenue to which it expects to be entitled for the transfer of promised goods or services to customers. ASU No. 2014-09 will replace most existing revenue recognition guidance in U.S. GAAP when it becomes effective. The new standard is effective January 1, 2018 for public companies. Early application is permitted as of January 1, 2017. The standard permits the use of either the retrospective or cumulative effect transition method. In March 2016, the FASB issued ASU No. 2016-08, Revenue from Contracts with Customers (Topic 606): Principal versus Agent Considerations (Reporting Revenue Gross versus Net), which clarifies the implementation guidance on principal versus agent considerations in ASU No. 2014-09. In April 2016, the FASB issued ASU No. 2016-10, Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing, which clarifies certain aspects of identifying performance obligations and licensing implementation guidance. In May 2016, the FASB issued ASU No. 2016-12, Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients, which relates to disclosures of remaining performance obligations, as well as other amendments to guidance on collectability, non-cash consideration and the presentation of sales and other similar taxes collected from customers. These standards have the same effective date and transition date of January 1, 2018. The Company adopted this guidance on January 1, 2018. The adoption of this guidance did not have a material impact on its condensed financial statements as the Company is not yet generating revenues. In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842), which requires lessees to recognize leases on-balance sheet and disclose key information about leasing arrangements. Topic 842 was subsequently amended by ASU No. 2018-01, Land Easement Practical Expedient for Transition to Topic 842; ASU No. 2018-10, Codification Improvements to Topic 842, Leases; and ASU No. 2018-11, Targeted Improvements. The new standard establishes a right-of-use (ROU) model that requires a lessee to recognize an ROU asset and lease liability on the balance sheet. Leases will be classified as finance or operating, with classification affecting the pattern and classification of expense recognition in the statement of operations. The Company adopted the new standard on January 1, 2019 and chose to apply the provisions of ASC 842 as of the effective date with no restatement of prior periods. Additionally, the Company has elected the ‘package of practical expedients’, which permit it not to reassess under the new standard its prior conclusions about lease identification, lease classification and initial direct costs. The Company did not elect the use-of-hindsight or the practical expedient pertaining to land easements; the latter is not applicable to the Company. The Company determines if an arrangement is a lease at inception and accounts for lease and non-lease components separately. The Company has elected not to apply the recognition requirements of Topic 842 for leases with a term of 12 months or less. Upon adoption of ASU 2016-02, the Company recognized an operating lease, right-of-use asset of $2.8 million and a corresponding liability of $3.8 million and eliminated $1.0 million of deferred rent in the Company’s condensed balance sheet. The adoption of ASU 2016-02 did not have any impact on the Company’s condensed statements of operations and comprehensive loss. See also Note 11. In May 2017, the FASB issued ASU No 2017-09, Compensation—Stock Compensation (Topic 718) — Scope of Modification Accounting, to clarify when to account for a change to the terms or conditions of a share-based payment award as a modification. Under the new standard, modification is required only if the fair value, the vesting conditions, or the classification of an award as equity or liability changes as a result of the change in terms or conditions. ASU 2017-09 was effective for the Company beginning January 1, 2018 and is applied prospectively. Early adoption is permitted. The Company adopted this guidance on January 1, 2018. The adoption of this guidance did not have a material impact on its financial statements as the Company has not made any changes to the terms or conditions of its share-based payment awards.

Net Loss per Share

Net Loss per Share	12 Months Ended
	Dec. 31, 2019
Net Loss per Share
Net Loss per Share	3. Net Loss per Share The following table shows the calculation of net loss per share (in thousands, except share and per share data): Year Ended December 31, 2019 2018 2017 Numerator: Net loss - basic and diluted $ (46,672) $ (46,939) $ (55,663) Denominator: Weighted average common shares outstanding 29,364,535 27,686,909 20,958,557 Less: weighted average common shares subject to repurchase (14,725) (176,949) (470,051) Weighted average common shares outstanding used to compute basic and diluted net loss per share 29,349,810 27,509,960 20,488,506 Net loss per share, basic and diluted $ (1.59) $ (1.71) $ (2.72) The amounts in the table below were excluded from the calculation of diluted net loss per share, due to their anti-dilutive effect: Year Ended December 31, 2019 2018 2017 Common stock subject to repurchase — 43,076 319,203 Outstanding options 5,643,410 3,778,259 3,013,394 Total shares of common stock equivalents 5,643,410 3,821,335 3,332,597

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2019
Fair Value Measurements
Fair Value Measurements	4. Fair Value Measurements Financial assets and liabilities are measured and recorded at fair value. The Company is required to disclose information on all assets and liabilities reported at fair value that enables an assessment of the inputs used in determining the reported fair values. The fair value hierarchy prioritizes valuation inputs based on the observable nature of those inputs. The fair value hierarchy applies only to the valuation inputs used in determining the reported fair value of the investments and is not a measure of the investment credit quality. The hierarchy defines three levels of valuation inputs: · Level 1—Quoted prices in active markets for identical assets or liabilities · Level 2—Inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly · Level 3—Unobservable inputs that reflect the Company’s own assumptions about the assumptions market participants would use in pricing the asset or liability There have been no transfers of assets and liabilities between levels of hierarchy. The Company’s Level 2 investments are valued using third-party pricing sources. The pricing services utilize industry standard valuation models, including both income and market-based approaches, for which all significant inputs are observable, either directly or indirectly, to estimate fair value. These inputs include reported trades of and broker/dealer quotes on the same or similar investments, issuer credit spreads, benchmark investments, prepayment/default projections based on historical data and other observable inputs. The following tables present information as of December 31, 2019 and 2018 about the Company’s assets that are measured at fair value on a recurring basis and indicate the level of the fair value hierarchy the Company utilized to determine such fair values (in thousands): December 31, 2019 Fair Value Measured Using Total (Level 1) (Level 2) (Level 3) Balance Assets Cash equivalents $ 4,252 $ — $ — $ 4,252 Marketable securities 7,023 65,805 — 72,828 $ 11,275 $ 65,805 $ — $ 77,080 December 31, 2018 Fair Value Measured Using Total (Level 1) (Level 2) (Level 3) Balance Assets Cash equivalents $ 38,698 $ — $ — $ 38,698 Marketable securities — 75,401 — 75,401 $ 38,698 $ 75,401 $ — $ 114,099 As of December 31, 2019, marketable securities had a maximum remaining maturity of ten months. As of December 31, 2019 and 2018, the fair value of available for sale marketable securities by type of security were as follows (in thousands): December 31, 2019 Gross Gross Amortized Unrealized Unrealized Fair Cost Gains Losses Value U.S. Treasury securities $ 7,019 $ 4 $ — $ 7,023 U.S. Government agency securities 17,701 16 — 17,717 Corporate debt obligations 48,079 17 (8) 48,088 $ 72,799 $ 37 $ (8) $ 72,828 December 31, 2018 Gross Gross Amortized Unrealized Unrealized Fair Cost Gains Losses Value U.S. Government agency securities $ 49,124 $ — $ (27) $ 49,097 Corporate debt obligations 26,311 — (7) 26,304 $ 75,435 $ — $ (34) $ 75,401

License and Collaboration Agree

License and Collaboration Agreements	12 Months Ended
	Dec. 31, 2019
License and Collaboration Agreements
License and Collaboration Agreements	5. License and Collaboration Agreements Scripps Licensing Agreement In December 2014, the Company entered into a license agreement with The Scripps Research Institute (“Scripps”), pursuant to which it was granted a non-exclusive, world-wide license for all fields of use under Scripps’ rights in certain know-how and technology related to a mouse hybridoma clone expressing an anti-human CD73 antibody, and to progeny, mutants or unmodified derivatives of such hybridoma and any antibodies expressed by such hybridoma, from which we developed CPI-006. Scripps also granted the Company the right to grant sublicenses in conjunction with other proprietary rights the Company holds, or to others collaborating with or performing services for the Company. Under this license agreement, Scripps has agreed not to grant any additional commercial licenses with respect to such materials, other than march-in rights granted to the U.S. government. Upon execution of the agreement, the Company made a one‑time cash payment to Scripps of $10,000 in 2015 and is also obligated to pay a minimum annual fee to Scripps of $25,000. The one‑time cash payment was recorded as research and development expense as technological feasibility of the asset had not been established and there was no alternative future use. A minimum annual fee payment is due on each anniversary of the effective date of the agreement for the term of the agreement. The Company is also required to make performance‑based cash payments upon successful completion of clinical and sales milestones. The aggregate potential milestone payments are $2.6 million. The Company is also required to pay royalties on net sales of licensed products (including CPI-006) sold by it, its affiliates and its sublicensees at a rate in the low‑single digits. In addition, should the Company sublicense the rights licensed under the agreement, it has agreed to pay a percentage of sublicense revenue received at specified rates that start at double digit percentages and decrease to single digit percentages based on the elapsed time from the effective date of the agreement and the time of entry into such sublicense. To date, no milestone payments have been made. The Company’s license agreement with Scripps will terminate upon expiration of its obligation to pay royalties to Scripps under the license agreement. The Company’s license agreement with Scripps is terminable by the consent of the parties, at will by the Company upon providing 90 days written notice to Scripps, or by Scripps for certain material breaches, or if the Company undergoes a bankruptcy event. In addition, Scripps may terminate the license on a product‑by‑product basis, or the entire agreement, if the Company fails to meet specified diligence obligations related to the development and commercialization of licensed products. Scripps may also terminate the agreement after the third anniversary of the effective date of the agreement if it reasonably believes, based on reports the Company provides to Scripps, that the Company has not used commercially reasonable efforts as required under the agreement, subject to a specified notice and cure period. Vernalis Licensing Agreement In February 2015, the Company entered into a license agreement with Vernalis (R&D) Limited (“Vernalis”), which was subsequently amended as of November 5, 2015, and, pursuant to which the Company was granted an exclusive, worldwide license under certain patent rights and know-how, including a limited right to grant sublicenses, for all fields of use to develop, manufacture and commercialize products containing certain adenosine receptor antagonists, including ciforadenant. Pursuant to this agreement, the Company made a one-time cash payment to Vernalis in the amount of $1.0 million, which was recorded as research and development expense as technological feasibility of the asset had not been established and there was no alternative future use. The Company is also required to make cash milestone payments to Vernalis upon the successful completion of clinical and regulatory milestones for licensed products depending on the indications for which such licensed products are developed and upon achievement of certain sales milestones. In February 2017, the Company made a milestone payment of $3.0 million to Vernalis following the expansion of a cohort of patients with renal cell cancer treated with single agent ciforadenant in the Company’s Phase 1/1b clinical trial. The aggregate potential milestone payments are approximately $220 million for all The Company has also agreed to pay Vernalis tiered incremental royalties based on the annual net sales of licensed products containing ciforadenant on a product‑by‑product and country‑by‑country basis, subject to certain offsets and reductions. The tiered royalty rates for products containing ciforadenant range from the mid‑single digits up to the low‑double digits on a country‑by‑country net sales basis. The royalties on other licensed products that do not include ciforadenant also increase with the amount of net sales on a product-by-product and country‑by‑country basis and range from the low‑single digits up to the mid‑single digits on a country‑by‑country net sales basis. The Company is also obligated to pay to Vernalis certain sales milestones as indicated above when worldwide net sales reach specified levels over an agreed upon time period. The agreement will expire on a product‑by‑product and country‑by‑country basis upon the expiration of the Company’s payment obligations to Vernalis in respect of a particular product and country. Both parties have the right to terminate the agreement for an uncured material breach by the other party. The Company may also terminate the agreement at its convenience by providing 90 days written notice, provided that the Company has not received notice of its own default under the agreement at the time the Company exercises such termination right. Vernalis may also terminate the agreement if the Company challenges a licensed patent or undergoes a bankruptcy event. Genentech Collaboration Agreement In October 2015, the Company entered into a clinical trial collaboration agreement with Genentech to evaluate the safety, tolerability and preliminary efficacy of ciforadenant combined with Genentech’s investigational cancer immunotherapy, Tecentriq (atezolizumab), a fully humanized monoclonal antibody targeting protein programmed cell death ligand 1(“PD-L1”), in a variety of solid tumors in a Phase 1/1b clinical trial. Pursuant to this agreement, the Company will be responsible for the conduct and cost of the relevant studies, under the supervision of a joint development committee made up of representatives of the Company and representatives of Genentech. Genentech will supply Tecentriq. As part of the agreement, the Company granted Genentech certain rights of first negotiation to participate in future clinical trials that the Company may conduct evaluating the administration of ciforadenant in combination with an anti-PD-1 or anti-PD-L1 antibody. If the Company and Genentech do not reach agreement on the terms of any such participation by Genentech within a specified time period, the Company retains the right to collaborate with third parties in such activities. The Company also granted Genentech certain rights of first negotiation should it decide to license development and commercialization rights to ciforadenant. Should the Company and Genentech not reach agreement on the terms of such a license within a specified time period, it retains the right to enter into a license with another third party. The Company and Genentech each have the right to terminate the agreement for material breach by the other party. In addition, the agreement may be terminated by either party due to safety considerations, if directed by a regulatory authority or if development of ciforadenant or Tecentriq is discontinued. Further, the agreement will expire after a set period of time following the provision by the Company of the final clinical study report to Genentech. In May, 2017, the Company signed a second clinical trial collaboration agreement with Genentech. Under the second agreement, ciforadenant administered in combination with Tecentriq is being evaluated in a Phase 1b/2 randomized, controlled clinical study, known as Morpheus, as second-line therapy in patients with non-small cell lung cancer who are resistant and/or refractory to prior therapy with an anti-PD-(L)1 antibody. The patients in the Morpheus trial are currently in the follow-up phase of the trial. Genentech is responsible for the conduct of the study and the parties share the cost of the Morpheus trial, which began enrolling patients in the fourth quarter of 2017. The Company is responsible for supplying ciforadenant and retains global development and commercialization rights to ciforadenant. The Company and Genentech each have the right to terminate the agreement for material breach by the other party. In addition, the agreement may be terminated by either party due to safety considerations, if directed by a regulatory authority or if development of ciforadenant or Tecentriq is discontinued. Monash License Agreement In April 2017, the Company entered into a license agreement with Monash University (Monash), pursuant to which the Company was granted an exclusive, sublicensable worldwide license under certain know‑how, patent rights and other intellectual property rights controlled by Monash to research, develop, and commercialize certain antibodies directed to CXCR2 for the treatment of human diseases. Upon execution of the agreement, the Company made a one‑time cash payment to Monash of $275,000 and reimbursed Monash for certain patent prosecution costs incurred prior to execution of the agreement. The Company us also obligated to pay an annual license maintenance fee to Monash of $25,000 until a certain development milestone is met with respect to the licensed product, after which no further maintenance fee will be due. The Company is also required to make development and sales milestone payments to Monash with respect to the licensed products in the aggregate of up to $45.1 million. The Company is also required to pay to Monash tiered royalties on net sales of licensed products sold by it, its affiliates and its sublicensees at a rate ranging in the low‑single digits. In addition, should the Company sublicense its rights under the agreement, the Company has agreed to pay a percentage of sublicense revenue received at specified rates that are currently at low double digit percentages and decrease to single digit percentages based on the achievement of development milestones. The term of the Company’s agreement with Monash continues until the expiration of its obligation to pay royalties to Monash thereunder. The license agreement is terminable at will by the Company upon providing 30 days written notice to Monash, or by either party for material breaches by the other party. In addition, Monash may terminate the entire agreement or convert the license to a non-exclusive license if the Company has materially breached our obligation to use commercially reasonable efforts to develop and commercialize a licensed product, subject to a specified notice and cure mechanism.

Balance Sheet Components

Balance Sheet Components	12 Months Ended
	Dec. 31, 2019
Balance Sheet Components
Balance Sheet Components	6. Balance Sheet Components (in thousands): December 31, 2019 2018 Prepaid and Other Current Assets Interest receivable $ 329 $ 337 Prepaid research and development manufacturing expenses 240 75 Prepaid facility expenses 157 149 Prepaid insurance 150 166 Other 486 265 $ 1,362 $ 992 Property and Equipment Laboratory equipment $ 2,396 $ 2,371 Computer equipment and purchased software 142 142 Leasehold improvements 2,084 2,084 4,622 4,597 Less: accumulated depreciation and amortization (3,160) (2,417) $ 1,462 $ 2,180 Accrued and Other Liabilities Accrued clinical trial related $ 4,300 $ 2,718 Accrued manufacturing expense 696 1,077 Personnel related 1,624 649 Other 279 585 $ 6,899 $ 5,029 Other Liabilities Deferred rent $ — $ 869 $ — $ 869

Common Stock

Common Stock	12 Months Ended
	Dec. 31, 2019
Common Stock
Common Stock	7. Common Stock As of December 31, 2019, the amended and restated certificate of incorporation authorizes the Company to issue 290 million shares of common stock and 10 million shares of preferred stock. Each share of common stock is entitled to one vote. Common stockholders are entitled to dividends if and when declared by the board of directors. As of December 31, 2019, no dividends on common stock had been declared. The Company has reserved shares of common stock, for issuance as follows: December 31, 2019 2018 2017 Exchange warrants 1,458,000 — — Shares available for future option grants 1,704,183 2,486,637 2,576,535 Outstanding options 5,643,410 3,778,259 3,013,394 Unvested restricted common stock (founders and early exercise of stock options) — 43,076 319,203 Shares reserved for employee stock purchase plan 400,000 400,000 400,000 Total 9,205,593 6,707,972 6,309,132

Stock Option Plans

Stock Option Plans	12 Months Ended
	Dec. 31, 2019
Stock Option Plans
Stock Option Plans	8. Stock Option Plans In February 2014, the Company adopted the 2014 Equity Incentive Plan (the “2014 Plan”), which was subsequently amended in November 2014, July 2015 and September 2015, under which it granted incentive stock options (“ISOs”) or non-qualified stock options (“NSOs”). Terms of stock agreements, including vesting requirements, are determined by the board of directors or a committee authorized by the board of directors, subject to the provisions of the 2014 Plan. In general, awards granted by the Company vest over four years and have maximum exercise term of 10 years. The 2014 Plan provides that grants must be at an exercise price of 100% of fair market value of the Company’s common stock as determined by the board of directors on the date of the grant. In connection with the consummation of the IPO in March 2016, the 2016 Equity Incentive Award Plan (the “2016 Plan”), became effective. Under the 2016 Plan, incentive stock options, non-statutory stock options, stock purchase rights and other stock-based awards may be granted. Terms of stock agreements, including vesting requirements, are determined by the board of directors or a committee authorized by the board of directors, subject to the provisions of the 2016 Plan. In general, awards granted by the Company vest over four years and have maximum exercise term of 10 years. The 2016 Plan provides that grants must be at an exercise price of 100% of fair market value of the Company’s common stock as determined by the board of directors on the date of the grant. In conjunction with adopting the 2016 Plan, the 2014 Plan was terminated and no further awards will be granted under the 2014 Plan. Options outstanding under the 2014 Plan as of the effective date of the 2016 Plan that are forfeited or lapse unexercised may be re-issued under the 2016 Plan, up to a maximum of 1,136,229 shares. Activity under the Company’s stock option plans is set forth below: Options Outstanding Weighted ‑ Shares Average Available Number of Exercise for Grant Options Price Balance at December 31, 2018 2,486,637 3,778,259 $ 10.32 Additional shares authorized 1,170,000 — — Options granted (2,029,000) 2,029,000 3.61 Options exercised — (87,303) 0.28 Options forfeited 76,546 (76,546) 11.67 Balance at December 31, 2019 1,704,183 5,643,410 $ 8.05 The following table summarizes information about stock options outstanding at December 31, 2019 and 2018: Options Outstanding Options Vested at December 31, 2019 at December 31, 2019 Weighted Weighted Average Average Weighted Remaining Weighted Remaining Average Contractual Average Contractual Exercise Exercise Price Number Life (in Years) Exercise Price Number Life (in Years) Price $0.28 - $2.56 191,000 $ 0.36 184,730 $ 0.29 $3.01 - $4.65 2,027,500 $ 3.61 32,375 $ 4.64 $4.84 $7.59 1,061,522 $ 5.95 261,504 $ 5.98 $9.52 - $14.43 1,051,738 $ 10.83 593,596 $ 10.90 $15.00 - $16.70 1,311,650 $ 15.49 1,138,764 $ 15.40 5,643,410 $ 8.05 2,210,969 $ 11.66 Options Outstanding Options Vested at December 31, 2018 at December 31, 2018 Weighted Weighted Average Average Weighted Remaining Weighted Remaining Average Contractual Average Contractual Exercise Exercise Price Number Life (in Years) Exercise Price Number Life (in Years) Price $0.28 - $4.65 301,803 $ 0.72 261,373 $ 0.68 $5.94 - $9.52 1,101,750 $ 6.10 3,585 $ 8.92 $9.60 - $14.43 1,026,180 $ 10.89 269,731 $ 10.56 $15.00 - $16.70 1,348,526 $ 15.49 834,456 $ 15.37 3,778,259 $ 10.32 1,369,145 $ 11.60 The weighted average grant date fair value of options granted for the years ended December 31, 2019, 2018 and 2017, was $2.53, $5.23 and $8.93, respectively. Options outstanding and exercisable that had vested or were expected to vest at December 31, 2019 were as follows: Weighted Average Aggregate Weighted Remaining Intrinsic Number Average Contractual Value of shares Exercise Price Life (years) (in thousands) Vested 2,210,969 $ 11.66 $ 977,587 Expected to vest 3,432,441 $ 5.72 $ 3,713,778 In the table above, aggregate intrinsic value represents the difference between the exercise price of the options to purchase common stock and the estimated fair value of the Company’s common stock of $5.44. The aggregate intrinsic value of stock options exercised in the years ended December 31, 2019, 2018 and 2017, was $0.4 million, $1.1 million and $0.3 million, respectively. The total fair value of options that vested in the year ended December 31, 2019, 2018 and 2017, was $7.8 million, $7.1 million, and $5.8 million, respectively.

Stock-Based Compensation

Stock-Based Compensation	12 Months Ended
	Dec. 31, 2019
Stock-Based Compensation
Stock-Based Compensation	9. Stock‑Based Compensation The Company’s results of operations include expenses relating to stock‑based awards as follows (in thousands): Year Ended December 31, 2019 2018 2017 Research and development $ 3,103 $ 2,919 $ 2,692 General and administrative 4,245 4,216 3,537 Total $ 7,348 $ 7,135 $ 6,229 Valuation Assumptions The Company estimated the fair value of employee stock options using the Black-Scholes valuation model. The fair value of employee stock options is being amortized on a straight-line basis over the requisite service period of the awards. The fair value of employee stock options were estimated using the following assumptions for the years ended December 31, 2019, 2018 and 2017: Year Ended December 31, 2019 2018 2017 Risk-free interest rate 1.9 % 2.8 % 2.1 % Expected volatility 82.1 % 82.7 % 91.4 % Expected term (in years) 6.0 6.0 6.0 Expected dividend yield 0 % 0 % 0 % Risk-free Interest Rate: The Company based the risk-free interest rate over the expected term of the options based on the constant maturity rate of U.S. Treasury securities with similar maturities as of the date of the grant. Volatility : The Company used an average historical stock price volatility of comparable public companies within the biotechnology and pharmaceutical industry that have been identified as the Company’s industry peers. Expected Term: The Company uses the simplified method prescribed in the ASC 718, Compensation—Stock Compensation, to calculate the expected term of options granted to employees and directors. Expected Dividends: The Company has not paid and does not anticipate paying any dividends in the near future. At December 31, 2019, 2018 and 2017, the unrecognized compensation expense associated with respect to options granted to employees was $13.4 million, $15.8 million and $18.6 million, respectively, and is expected to be recognized on a straight‑line basis over 2.71, 2.72, and 2.85 years, respectively.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2019
Income Taxes
Income Taxes	10. Income Taxes The components of loss before income tax is as follows (in thousands): December 31, 2019 2018 2017 Domestic $ (46,672) $ (47,096) $ (28,253) Foreign — 157 (27,410) $ (46,672) $ (46,939) $ (55,663) During the years ended December 31, 2019, 2018 and 2017, the Company recorded no income tax benefits for the net operating losses (NOLs) incurred due to the uncertainty of realizing a benefit from those items. A reconciliation of the Company’s effective tax rate to the U.S. Federal statutory rate is as follows: December 31, 2019 2018 2017 Federal tax benefit at statutory rate 21 % 21 % 34 % State tax, net of Federal benefit 6 % 9 % 7 % Foreign rate differential — — % (17) % Federal rate change impact — — % (9) Change in valuation allowance (28) % (41) % (16) % Research and development tax credits 3 % 2 % 2 % Prior year federal true-up — % 10 % (3) % Other (2) % (1) % 2 Effective income tax rate % % % The effective tax rate is different from the federal statutory tax rate primarily due to a foreign rate differential and a valuation allowance against deferred tax assets as a result of the Company’s history of losses. The principal components of the Company’s net deferred tax assets are as follows (in thousands) December 31, 2019 2018 2017 Deferred tax assets Net operating loss carryforwards $ 42,486 $ 31,533 $ 15,438 Tax credit carryforwards 6,990 6,441 4,351 Capitalized tax assets (3) 138 131 Accruals 152 188 183 Stock compensation 4,317 2,879 1,730 Operating lease liability 892 — — Other 40 58 52 Total deferred tax assets $ 54,874 $ 41,237 $ 21,885 Deferred tax liabilities Operating lease right-of-use asset $ (651) $ — $ — Valuation allowance (54,223) (41,237) (21,885) Net deferred tax assets $ — $ — $ — The Company recorded a valuation allowance against its deferred tax assets at December 31, 2019 and 2018 because Company management believed that it was more likely than not that these assets would not be fully realized in the future. The valuation allowance increased by approximately $13.0 million and $19.4 million for the years ended December 31, 2019 and 2018, respectively. Changes in the valuation allowance for deferred tax assets relate primarily to the increase in the Company’s net operating loss carryforward. As of December 31, 2019, the Company had federal NOL carryforwards of approximately $144.5 million and state NOL carryforwards of approximately $173.9 million which are available to reduce future taxable income. The NOLs will begin to expire in 2034, if not utilized. Utilization of the net operating loss carryforwards are subject to various limitations due to the ownership change limitations provided by Internal Revenue Code (IRC) Section 382 and similar state provisions. As of December 31, 2019, the Company also had $6.1 million of federal and $3.3 million of state research and development tax credit carryforwards available to reduce future income taxes. The federal research and development tax credits will begin to expire 2035, if not utilized. The state research and development tax credits have no expiration date. As of December 31, 2019, the Company had unrecognized tax benefits (“UTBs”) of approximately $1.9 million. All of the deferred tax assets associated with these UTBs are fully offset by a valuation allowance. The following table summarizes the activity related to UTBs: December 31, 2019 2018 2017 Unrecognized tax benefits beginning of the period $ 1,804 $ 1,219 $ 604 Decrease related to the prior year (365) — (51) Increased related to the current year 446 585 666 Unrecognized tax benefits, end of the period $ 1,885 $ 1,804 $ 1,219 The Company follows the provisions of ASC 740, Accounting for Income Taxes, and the accounting guidance related to accounting for uncertainty in income taxes. The Company determines its uncertain tax positions based on a determination of whether and how much of a tax benefit taken by the Company in its tax filings or positions is more likely than not to be sustained upon examination by the relevant income tax authorities. None of the Company’s unrecognized tax benefits that, if recognized, would affect its effective tax rate. The Company does not anticipate the total amounts of unrecognized tax benefits will significantly increase or decrease in the next 12 months. The Company will recognize both accrued interest and penalties related to unrecognized benefits in income tax expense. Management determined that no accrual for interest or penalties was required as of December 31, 2019, 2018 and 2017. The Company currently has no federal or state tax examinations in progress nor has it had any federal or state examinations since inception. As a result of the Company’s net operating loss carryforwards, all of its tax years are subject to federal and state tax examinations.

Facility Lease

Facility Lease	12 Months Ended
	Dec. 31, 2019
Facility Lease
Facility lease	11. Facility Lease In January 2015, the Company signed an initial operating lease, effective February 1, 2015 for 8,138 square feet of office and laboratory space with a one year term. Between January 2015 and October 2018, the Company entered into a series of lease amendments to increase the amount of leased space to 27,280 square feet and extend the expiration of the lease to February 2023. The lease agreement includes annual rent escalations. Under the lease and subsequent amendments, the landlord provided approximately $1.9 million in free rent and lease incentives. The Company records rent expense on a straight-line basis over the effective term of the lease, including any free rent periods and incentives. As the interest rate implicit in lease arrangements is typically not readily available, in calculating the present value of the lease payments, the Company has utilized its incremental borrowing rate, which is determined based on the prevailing market rates for collateralized debt with maturity dates commensurate with the term of its lease . The Company’s facility lease is a net lease, as the non-lease components (i.e. common area maintenance) are paid separately from rent based on actual costs incurred. Therefore, the non-lease components were not included in the right-of-use asset and liability and are reflected as an expense in the period incurred. As of December 31, 2019 and 2018, the right-of-use asset under operating lease was $2.3 million and $0, respectively. The elements of lease expense were as follows (in thousands): Statements of operations and Year Ended December 31, comprehensive loss location 2019 2018 2017 Costs of operating lease Operating lease costs Research and development, $ 960 $ 748 $ 734 Costs of non-lease components (previously common area maintenance) Research and development, 324 296 281 Total operating lease cost $ 1,284 $ 1,044 $ 1,015 Other Information Operating cash flows used for operating lease $ 1,449 $ 1,389 $ 1,398 Remaining lease term 3.1 years 4.1 years 3.1 years Discount rate — — As of December 31, 2019, minimum rental commitments under this lease were as follows (in thousands) Year Ended December 31 (in thousands) 2020 $ 1,159 2021 1,260 2022 1,299 Total lease payments 3,718 Less: imputed interest (530) Total $ 3,188 As of December 31, 2018, minimum rental commitments under this lease were as follows (in thousands) Year Ended December 31 (in thousands) 2019 $ 1,110 2020 1,142 2021 1,251 2022 1,296 2023 109 Total $ 4,908

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2019
Commitments and Contingencies
Commitments and Contingencies	12. Commitments and Contingencies In August 2015 the Company entered into an agreement for a line of credit of $0.1 million for the purpose of issuing its landlord a letter of credit of $0.1 million as a security deposit under its facility lease. The Company pledged money market funds and marketable securities as collateral for the line of credit. For further discussion of the Company’s facility lease agreement, see Note 11. Pursuant to the Company’s license agreements with each of Vernalis and Scripps, it has obligations to make future milestone and royalty payments to these parties, respectively. However, because these amounts are contingent, they have not been included on the Company’s balance sheet. For further discussion of the Vernalis and Scripps licensing agreements, see Note 5. Indemnifications In the ordinary course of business, the Company enters into agreements that may include indemnification provisions. Pursuant to such agreements, the Company may indemnify, hold harmless and defend an indemnified party for losses suffered or incurred by the indemnified party. Some of the provisions will limit losses to those arising from third‑party actions. In some cases, the indemnification will continue after the termination of the agreement. The maximum potential amount of future payments the Company could be required to make under these provisions is not determinable. The Company has never incurred material costs to defend lawsuits or settle claims related to these indemnification provisions. The Company has also entered into indemnification agreements with its directors and officers that may require the Company to indemnify its directors and officers against liabilities that may arise by reason of their status or service as directors or officers to the fullest extent permitted by Delaware corporate law. There have been no claims to date and the Company has a directors and officers insurance policy that may enable it to recover a portion of any amounts paid for future claims. Legal Proceedings The Company is not a party to any material legal proceedings.

Related Party Transaction

Related Party Transaction	12 Months Ended
	Dec. 31, 2019
Related Party Transaction
Related Party Transaction	13. Related Party Transactions In 2017, the Company purchased $461,000 of research services from a vendor during the normal course of business, where a Corvus director is also a member of the vendor's board of directors. In March 2018, the Company completed a follow-on public offering in which the Company sold 8,117,647 shares of common stock at a price of $8.50 per share, which included 1,058,823 shares issued pursuant to the underwriters’ exercise of their option to purchase additional shares of common stock. The aggregate net proceeds received by the Company from the offering were approximately $64.9 million, net of underwriting discounts and commissions and offering expenses payable by the Company. The following aggregate number of shares of common stock were sold to our owners of more than 5% of our common stock, directors, or executive officers during the March 2018 underwritten public offering: March 2018 Public Offering Number of Aggregate Shares of Purchase Common Stock Price Owners of More Than 5% of Our Common Stock FMR LLC 1,176,470 $ 9,999,995 OrbiMed Advisors LLC (1) 588,235 4,999,998 Novo Holdings A/S (2) 1,176,470 9,999,995 Adams Street Partners (3) 588,235 4,999,998 Board of Directors Richard A. Miller, M.D. 100,000 850,000 (1) Peter Thompson, M.D., a member of our Board of Directors since November 2014, is a Private Equity Partner at OrbiMed Advisors, LLC. (2) Peter Moldt, Ph.D., a Partner at Novo Ventures (US) Inc., which provide certain consultancy services to Novo Holdings A/S, served as a member of our Board of Directors from January 2015 to January 2019. (3) Elisha P. (Terry) Gould III, a member of our Board of Directors since November 2014, is a Partner at Adams Street Partners, LLC.

Quarterly Selected Financial Da

Quarterly Selected Financial Data (unaudited)	12 Months Ended
	Dec. 31, 2019
Quarterly Selected Financial Data (unaudited)
Quarterly Selected Financial Data (unaudited)	14. Quarterly Selected Financial Data (unaudited) Quarter Ended December 31, September 30, June 30, March 31, (in thousands, except per share amounts) 2019 2019 2019 2019 Operating expenses $ 11,440 $ 11,513 $ 13,596 $ 12,305 Net loss (11,047) (11,004) (12,978) (11,643) Net loss per share, basic and diluted $ (0.38) $ (0.37) $ (0.44) $ (0.40) Quarter Ended December 31, September 30, June 30, March 31, (in thousands, except per share amounts) 2018 2018 2018 2018 Operating expenses $ 11,171 $ 11,149 $ 12,258 $ 14,644 Net loss (10,509) (10,498) (11,631) (14,301) Net loss per share, basic and diluted $ (0.36) $ (0.36) $ (0.40) $ (0.63)

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2019
Summary of Significant Accounting Policies
Basis of Presentation	Basis of Presentation The accompanying financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“U.S. GAAP”). The Company’s functional and reporting currency is the U.S. dollar. The accompanying financial statements have been prepared on a going-concern basis, which contemplates the realization of assets and discharge of liabilities in the normal course of business. Since its inception, the Company has incurred significant losses and negative cash flows from operations. As of December 31, 2019, the Company had an accumulated deficit of $217.1 million and cash, cash equivalents and marketable securities of $78.0 million. The Company has financed its operations primarily with the proceeds from the sale of stock. The Company will need to raise additional capital to meet its business objectives. The Company believes that its current cash, cash equivalents and marketable securities will be sufficient to fund its planned expenditures and meet its obligations through at least the next twelve months from the issuance of these financial statements.
Use of Estimates	Use of Estimates The preparation of the Company’s financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. Actual results could differ from such estimates.
Concentrations of Credit Risk and Other Risks and Uncertainties	Concentrations of Credit Risk and Other Risks and Uncertainties Substantially all of the Company’s cash and cash equivalents are deposited in accounts with two financial institutions that management believes are of high credit quality. Such deposits may, at times, exceed federally insured limits. The Company maintains its cash with an accredited financial institution and accordingly, such funds are subject to minimal credit risk. The Company’s marketable securities consist of investments in U.S. Treasury securities, U.S. government agency securities and corporate debt obligations, which can be subject to certain credit risks. However, the Company mitigates the risks by investing in high-grade instruments, limiting its exposure to any one issuer, and monitoring the ongoing creditworthiness of the financial institutions and issuers. The Company has not experienced any losses on its deposits of cash, cash equivalents or marketable securities. The Company is subject to a number of risks similar to other early stage biopharmaceutical companies, including, but not limited to, the need to obtain adequate additional funding, possible failure of preclinical testing or clinical trials, its reliance on third parties to conduct its clinical trials, the need to obtain marketing approval for its product candidates, competitors developing new technological innovations, the need to successfully commercialize and gain market acceptance of the Company’s product candidates, its right to develop and commercialize its product candidates pursuant to the terms and conditions of the licenses granted to the Company, and protection of proprietary technology. If the Company does not successfully commercialize or partner any of its product candidates, it will be unable to generate product revenue or achieve profitability.
Segments	Segments Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision‑maker in making decisions regarding resource allocation and assessing performance. The Company views its operations and manages its business in one operating segment, that of the development of and commercialization of precisely targeted oncology therapies.
Cash and Cash Equivalents and Marketable Securities	Cash, Cash Equivalents and Marketable Securities The Company considers all highly liquid investment securities with remaining maturities at the date of purchase of three months or less to be cash equivalents. Investments with remaining maturities, at the date of purchase, greater than three months are classified as “available-for-sale” and are carried at fair value with unrealized gains and losses, if any, included as a component of accumulated other comprehensive income (loss) in stockholders’ equity. Interest and realized gains and losses are included in interest income. Realized gains and losses are recognized based on the specific identification model.
Fair Value Measurements	Fair Value Measurements Fair value accounting is applied for all financial assets and liabilities and non-financial assets and liabilities that are recognized or disclosed at fair value in the financial statements on a recurring basis (at least annually). The carrying amount of the Company’s financial instruments, including cash equivalents, accounts payable and accrued liabilities, approximate fair value due to their short-term maturities.
Property and Equipment, Net	Property and Equipment, Net Property and equipment are stated at cost and depreciated using the straight‑line method over the estimated useful lives of the respective assets: Laboratory equipment years Computer equipment and purchased software years Leasehold improvements Shorter of asset's useful life or remaining term of lease Maintenance and repairs that do not extend the life or improve the asset are expensed when incurred. When assets are retired or otherwise disposed of, the cost and accumulated depreciation or amortization are removed from the balance sheet and any resulting gain or loss is reflected in operations.
Impairment of Long-Lived Assets	Impairment of Long‑Lived Assets The Company regularly reviews the carrying value and estimated lives of all of its long-lived assets, including property and equipment, to determine whether indicators of impairment may exist which warrant adjustments to carrying values or estimated useful lives. The determinants used for this evaluation include management’s estimate of the asset’s ability to generate positive income from operations and positive cash flow in future periods as well as the strategic significance of the assets to the Company’s business objectives. Should impairment exist, the impairment loss to be recognized is measured by the amount by which the carrying amount of the asset exceeds the projected discounted future net cash flows arising from the asset. All long-lived assets are maintained in the United States of America.
Research and Development Expenses	Research and Development Expenses The Company records research and development expenses as incurred. The Company accounts for nonrefundable advance payments for goods and services that will be used in future research and development activities as expenses when the goods have been received or when the service has been performed rather than when the payment is made. Research and development expenses consist of costs incurred by the Company for the discovery and development of the Company’s product candidates and include: · employee‑related expenses, including salaries, benefits, travel and non‑cash stock‑based compensation expense; · external research and development expenses incurred under arrangements with third parties, such as contract research organizations, contract manufacturing organizations, academic and non‑profit institutions and consultants; · costs to acquire technologies to be used in research and development that have not reached technological feasibility and have no alternative future use; · license fees; and · other expenses, which include direct and allocated expenses for laboratory, facilities and other costs.
Clinical Trial Accruals	Clinical Trial Accruals Costs for preclinical studies and clinical trial activities are recognized based on an evaluation of the vendors’ progress towards completion of specific tasks, using data such as clinical site activations, patient enrollment or information provided to the Company by its vendors regarding their actual costs incurred. Payments for these activities are based on the terms of individual contracts and payment timing may differ significantly from the period in which the services are performed. The Company determines accrual estimates through reports from and discussions with applicable personnel and outside service providers as to the progress or state of completion, or the services completed. The Company’s estimates of accrued expenses as of each balance sheet date are based on the facts and circumstances known at the time.
Stock-Based Compensation	Stock‑Based Compensation The Company maintains incentive plans under which incentive stock options and nonqualified stock options may be granted to employees and non‑employee service providers. The Company accounts for stock-based employee compensation arrangements in accordance with the provisions of ASC 718, “Compensation—Stock Compensation.” For stock options granted to employees, the Company recognizes compensation expense for all stock-based awards based on the grant-date estimated fair values. The value of the award is recognized as an expense ratably over the requisite service period. The fair value of stock options is determined using the Black-Scholes option pricing model. Forfeitures are accounted for when they occur. Stock-based compensation expense related to stock options granted to non-employees is recognized based on the fair value of the stock options, determined using the Black-Scholes option pricing model. The awards generally vest over the time period the Company expects to receive service from the non-employee.
Income Taxes	Income Taxes The Company accounts for income taxes under the asset and liability method. The Company estimates actual current tax exposure together with assessing temporary differences resulting from differences in accounting for reporting purposes and tax purposes for certain items, such as accruals and allowances not currently deductible for tax purposes. These temporary differences result in deferred tax assets and liabilities, which are included in the Company’s balance sheets. In general, deferred tax assets represent future tax benefits to be received when certain expenses previously recognized in the Company’s statements of operations and comprehensive loss become deductible expenses, under applicable income tax laws or when net operating loss or credit carryforwards are utilized. Accordingly, realization of the Company’s deferred tax assets is dependent on future taxable income against which these deductions, losses and credits can be utilized. The Company must assess the likelihood that the Company’s deferred tax assets will be recovered from future taxable income and a valuation allowance is recorded when it is more likely than not that the deferred tax asset will not be recovered. The Company applies judgment in the determination of the financial statement recognition and measurement of a tax position taken or expected to be taken in a tax return. Based on the available evidence, the Company is unable, at this time, to support the determination that it is more likely than not that its deferred tax assets will be utilized in the future. Accordingly, the Company recorded a full valuation allowance for all periods presented. The Company intends to maintain a valuation allowance until sufficient evidence exists to support its reversal. The Company recognizes benefits of uncertain tax positions if it is more likely than not such positions will be sustained upon examination based solely on their technical merits as the largest amount of benefit that is more likely than not to be realized upon the ultimate settlement. The Company recognizes any material interest and penalties related to unrecognized tax benefits in income tax expense. The Company is required to file income tax returns in the U.S. federal jurisdiction. The Company currently is not under examination by the Internal Revenue Service or other jurisdictions for any tax years.
Comprehensive Loss	Comprehensive Loss Comprehensive loss includes net loss as well as other changes in stockholders’ equity that result from transactions and economic events other than those with stockholders. The Company’s only element of other comprehensive loss in any period presented was unrealized gains and losses on available-for-sale marketable securities.
Net Loss per Share	Net Loss per Share Basic net loss per share is calculated by dividing the net loss by the weighted average number of common shares outstanding and Exchange Warrants outstanding during the period, without consideration of potentially dilutive securities. In accordance with Accounting Standards Codification Topic 260, Earnings Per Share , the Exchange Warrants are included in the computation of basic net loss per share because the exercise price is negligible and they are fully vested and exercisable at any time after the original issuance date. Diluted net loss per share is computed by dividing the net loss by the weighted average number of common shares, Exchange Warrants, and potentially dilutive securities outstanding for the period. Diluted net loss per share is the same as basic net loss per share for all periods presented since the effect of potentially dilutive securities is anti-dilutive given the net loss of the Company.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2014-09, Revenue from Contracts with Customers, which required an entity to recognize the amount of revenue to which it expects to be entitled for the transfer of promised goods or services to customers. ASU No. 2014-09 will replace most existing revenue recognition guidance in U.S. GAAP when it becomes effective. The new standard is effective January 1, 2018 for public companies. Early application is permitted as of January 1, 2017. The standard permits the use of either the retrospective or cumulative effect transition method. In March 2016, the FASB issued ASU No. 2016-08, Revenue from Contracts with Customers (Topic 606): Principal versus Agent Considerations (Reporting Revenue Gross versus Net), which clarifies the implementation guidance on principal versus agent considerations in ASU No. 2014-09. In April 2016, the FASB issued ASU No. 2016-10, Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing, which clarifies certain aspects of identifying performance obligations and licensing implementation guidance. In May 2016, the FASB issued ASU No. 2016-12, Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients, which relates to disclosures of remaining performance obligations, as well as other amendments to guidance on collectability, non-cash consideration and the presentation of sales and other similar taxes collected from customers. These standards have the same effective date and transition date of January 1, 2018. The Company adopted this guidance on January 1, 2018. The adoption of this guidance did not have a material impact on its condensed financial statements as the Company is not yet generating revenues. In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842), which requires lessees to recognize leases on-balance sheet and disclose key information about leasing arrangements. Topic 842 was subsequently amended by ASU No. 2018-01, Land Easement Practical Expedient for Transition to Topic 842; ASU No. 2018-10, Codification Improvements to Topic 842, Leases; and ASU No. 2018-11, Targeted Improvements. The new standard establishes a right-of-use (ROU) model that requires a lessee to recognize an ROU asset and lease liability on the balance sheet. Leases will be classified as finance or operating, with classification affecting the pattern and classification of expense recognition in the statement of operations. The Company adopted the new standard on January 1, 2019 and chose to apply the provisions of ASC 842 as of the effective date with no restatement of prior periods. Additionally, the Company has elected the ‘package of practical expedients’, which permit it not to reassess under the new standard its prior conclusions about lease identification, lease classification and initial direct costs. The Company did not elect the use-of-hindsight or the practical expedient pertaining to land easements; the latter is not applicable to the Company. The Company determines if an arrangement is a lease at inception and accounts for lease and non-lease components separately. The Company has elected not to apply the recognition requirements of Topic 842 for leases with a term of 12 months or less. Upon adoption of ASU 2016-02, the Company recognized an operating lease, right-of-use asset of $2.8 million and a corresponding liability of $3.8 million and eliminated $1.0 million of deferred rent in the Company’s condensed balance sheet. The adoption of ASU 2016-02 did not have any impact on the Company’s condensed statements of operations and comprehensive loss. See also Note 11. In May 2017, the FASB issued ASU No 2017-09, Compensation—Stock Compensation (Topic 718) — Scope of Modification Accounting, to clarify when to account for a change to the terms or conditions of a share-based payment award as a modification. Under the new standard, modification is required only if the fair value, the vesting conditions, or the classification of an award as equity or liability changes as a result of the change in terms or conditions. ASU 2017-09 was effective for the Company beginning January 1, 2018 and is applied prospectively. Early adoption is permitted. The Company adopted this guidance on January 1, 2018. The adoption of this guidance did not have a material impact on its financial statements as the Company has not made any changes to the terms or conditions of its share-based payment awards.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2019
Summary of Significant Accounting Policies
Schedule of estimated useful lives of property and equipment, net	Laboratory equipment years Computer equipment and purchased software years Leasehold improvements Shorter of asset's useful life or remaining term of lease

Net Loss per Share (Tables)

Net Loss per Share (Tables)	12 Months Ended
	Dec. 31, 2019
Net Loss per Share
Schedule of net loss per share, basic and diluted	The following table shows the calculation of net loss per share (in thousands, except share and per share data): Year Ended December 31, 2019 2018 2017 Numerator: Net loss - basic and diluted $ (46,672) $ (46,939) $ (55,663) Denominator: Weighted average common shares outstanding 29,364,535 27,686,909 20,958,557 Less: weighted average common shares subject to repurchase (14,725) (176,949) (470,051) Weighted average common shares outstanding used to compute basic and diluted net loss per share 29,349,810 27,509,960 20,488,506 Net loss per share, basic and diluted $ (1.59) $ (1.71) $ (2.72)
Schedule of antidilutive securities excluded from calculation of diluted net loss per share	Year Ended December 31, 2019 2018 2017 Common stock subject to repurchase — 43,076 319,203 Outstanding options 5,643,410 3,778,259 3,013,394 Total shares of common stock equivalents 5,643,410 3,821,335 3,332,597

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2019
Fair Value Measurements
Schedule of fair value of assets measured at fair value on a recurring basis, by level of fair value hierarchy	The following tables present information as of December 31, 2019 and 2018 about the Company’s assets that are measured at fair value on a recurring basis and indicate the level of the fair value hierarchy the Company utilized to determine such fair values (in thousands): December 31, 2019 Fair Value Measured Using Total (Level 1) (Level 2) (Level 3) Balance Assets Cash equivalents $ 4,252 $ — $ — $ 4,252 Marketable securities 7,023 65,805 — 72,828 $ 11,275 $ 65,805 $ — $ 77,080 December 31, 2018 Fair Value Measured Using Total (Level 1) (Level 2) (Level 3) Balance Assets Cash equivalents $ 38,698 $ — $ — $ 38,698 Marketable securities — 75,401 — 75,401 $ 38,698 $ 75,401 $ — $ 114,099
Schedule of fair value of available for sale marketable securities	As of December 31, 2019 and 2018, the fair value of available for sale marketable securities by type of security were as follows (in thousands): December 31, 2019 Gross Gross Amortized Unrealized Unrealized Fair Cost Gains Losses Value U.S. Treasury securities $ 7,019 $ 4 $ — $ 7,023 U.S. Government agency securities 17,701 16 — 17,717 Corporate debt obligations 48,079 17 (8) 48,088 $ 72,799 $ 37 $ (8) $ 72,828 December 31, 2018 Gross Gross Amortized Unrealized Unrealized Fair Cost Gains Losses Value U.S. Government agency securities $ 49,124 $ — $ (27) $ 49,097 Corporate debt obligations 26,311 — (7) 26,304 $ 75,435 $ — $ (34) $ 75,401

Balance Sheet Components (Table

Balance Sheet Components (Tables)	12 Months Ended
	Dec. 31, 2019
Balance Sheet Components
Schedule of balance sheet components	Balance Sheet Components (in thousands): December 31, 2019 2018 Prepaid and Other Current Assets Interest receivable $ 329 $ 337 Prepaid research and development manufacturing expenses 240 75 Prepaid facility expenses 157 149 Prepaid insurance 150 166 Other 486 265 $ 1,362 $ 992 Property and Equipment Laboratory equipment $ 2,396 $ 2,371 Computer equipment and purchased software 142 142 Leasehold improvements 2,084 2,084 4,622 4,597 Less: accumulated depreciation and amortization (3,160) (2,417) $ 1,462 $ 2,180 Accrued and Other Liabilities Accrued clinical trial related $ 4,300 $ 2,718 Accrued manufacturing expense 696 1,077 Personnel related 1,624 649 Other 279 585 $ 6,899 $ 5,029 Other Liabilities Deferred rent $ — $ 869 $ — $ 869

Common Stock (Tables)

Common Stock (Tables)	12 Months Ended
	Dec. 31, 2019
Common Stock
Schedule of shares of common stock reserved for issuance	December 31, 2019 2018 2017 Exchange warrants 1,458,000 — — Shares available for future option grants 1,704,183 2,486,637 2,576,535 Outstanding options 5,643,410 3,778,259 3,013,394 Unvested restricted common stock (founders and early exercise of stock options) — 43,076 319,203 Shares reserved for employee stock purchase plan 400,000 400,000 400,000 Total 9,205,593 6,707,972 6,309,132

Stock Option Plans (Tables)

Stock Option Plans (Tables)	12 Months Ended
	Dec. 31, 2019
Stock Option Plans
Summary of stock option activity	Options Outstanding Weighted ‑ Shares Average Available Number of Exercise for Grant Options Price Balance at December 31, 2018 2,486,637 3,778,259 $ 10.32 Additional shares authorized 1,170,000 — — Options granted (2,029,000) 2,029,000 3.61 Options exercised — (87,303) 0.28 Options forfeited 76,546 (76,546) 11.67 Balance at December 31, 2019 1,704,183 5,643,410 $ 8.05
Summary of information about stock options outstanding	Options Outstanding Options Vested at December 31, 2019 at December 31, 2019 Weighted Weighted Average Average Weighted Remaining Weighted Remaining Average Contractual Average Contractual Exercise Exercise Price Number Life (in Years) Exercise Price Number Life (in Years) Price $0.28 - $2.56 191,000 $ 0.36 184,730 $ 0.29 $3.01 - $4.65 2,027,500 $ 3.61 32,375 $ 4.64 $4.84 $7.59 1,061,522 $ 5.95 261,504 $ 5.98 $9.52 - $14.43 1,051,738 $ 10.83 593,596 $ 10.90 $15.00 - $16.70 1,311,650 $ 15.49 1,138,764 $ 15.40 5,643,410 $ 8.05 2,210,969 $ 11.66 Options Outstanding Options Vested at December 31, 2018 at December 31, 2018 Weighted Weighted Average Average Weighted Remaining Weighted Remaining Average Contractual Average Contractual Exercise Exercise Price Number Life (in Years) Exercise Price Number Life (in Years) Price $0.28 - $4.65 301,803 $ 0.72 261,373 $ 0.68 $5.94 - $9.52 1,101,750 $ 6.10 3,585 $ 8.92 $9.60 - $14.43 1,026,180 $ 10.89 269,731 $ 10.56 $15.00 - $16.70 1,348,526 $ 15.49 834,456 $ 15.37 3,778,259 $ 10.32 1,369,145 $ 11.60
Schedule of options outstanding and exercisable that had vested or were expected to vest	Weighted Average Aggregate Weighted Remaining Intrinsic Number Average Contractual Value of shares Exercise Price Life (years) (in thousands) Vested 2,210,969 $ 11.66 $ 977,587 Expected to vest 3,432,441 $ 5.72 $ 3,713,778

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2019
Schedule of expenses relating to employee and non-employee stock-based awards	The Company’s results of operations include expenses relating to stock‑based awards as follows (in thousands): Year Ended December 31, 2019 2018 2017 Research and development $ 3,103 $ 2,919 $ 2,692 General and administrative 4,245 4,216 3,537 Total $ 7,348 $ 7,135 $ 6,229
Employee stock options
Schedule of fair value of share-based awards to employees was estimated using Black Scholes model	Year Ended December 31, 2019 2018 2017 Risk-free interest rate 1.9 % 2.8 % 2.1 % Expected volatility 82.1 % 82.7 % 91.4 % Expected term (in years) 6.0 6.0 6.0 Expected dividend yield 0 % 0 % 0 %

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2019
Income Taxes
Schedule of components of loss before income tax	The components of loss before income tax is as follows (in thousands): December 31, 2019 2018 2017 Domestic $ (46,672) $ (47,096) $ (28,253) Foreign — 157 (27,410) $ (46,672) $ (46,939) $ (55,663)
Schedule of reconciliation of the effective tax rate to the U.S. Federal statutory rate	December 31, 2019 2018 2017 Federal tax benefit at statutory rate 21 % 21 % 34 % State tax, net of Federal benefit 6 % 9 % 7 % Foreign rate differential — — % (17) % Federal rate change impact — — % (9) Change in valuation allowance (28) % (41) % (16) % Research and development tax credits 3 % 2 % 2 % Prior year federal true-up — % 10 % (3) % Other (2) % (1) % 2 Effective income tax rate % % %
Schedule of principal components of the net deferred tax assets	The principal components of the Company’s net deferred tax assets are as follows (in thousands) December 31, 2019 2018 2017 Deferred tax assets Net operating loss carryforwards $ 42,486 $ 31,533 $ 15,438 Tax credit carryforwards 6,990 6,441 4,351 Capitalized tax assets (3) 138 131 Accruals 152 188 183 Stock compensation 4,317 2,879 1,730 Operating lease liability 892 — — Other 40 58 52 Total deferred tax assets $ 54,874 $ 41,237 $ 21,885 Deferred tax liabilities Operating lease right-of-use asset $ (651) $ — $ — Valuation allowance (54,223) (41,237) (21,885) Net deferred tax assets $ — $ — $ —
Schedule of unrecognized tax benefits activity	December 31, 2019 2018 2017 Unrecognized tax benefits beginning of the period $ 1,804 $ 1,219 $ 604 Decrease related to the prior year (365) — (51) Increased related to the current year 446 585 666 Unrecognized tax benefits, end of the period $ 1,885 $ 1,804 $ 1,219

Facility Lease (Tables)

Facility Lease (Tables)	12 Months Ended
	Dec. 31, 2019
Facility Lease
Elements of lease expense	The elements of lease expense were as follows (in thousands): Statements of operations and Year Ended December 31, comprehensive loss location 2019 2018 2017 Costs of operating lease Operating lease costs Research and development, $ 960 $ 748 $ 734 Costs of non-lease components (previously common area maintenance) Research and development, 324 296 281 Total operating lease cost $ 1,284 $ 1,044 $ 1,015 Other Information Operating cash flows used for operating lease $ 1,449 $ 1,389 $ 1,398 Remaining lease term 3.1 years 4.1 years 3.1 years Discount rate — —
Minimum rental commitments	As of December 31, 2019, minimum rental commitments under this lease were as follows (in thousands) Year Ended December 31 (in thousands) 2020 $ 1,159 2021 1,260 2022 1,299 Total lease payments 3,718 Less: imputed interest (530) Total $ 3,188
Schedule of future minimum lease payments under Topic 840	As of December 31, 2018, minimum rental commitments under this lease were as follows (in thousands) Year Ended December 31 (in thousands) 2019 $ 1,110 2020 1,142 2021 1,251 2022 1,296 2023 109 Total $ 4,908

Related Party Transaction (Tabl

Related Party Transaction (Tables)	12 Months Ended
	Dec. 31, 2019
Related Party Transaction
Schedule of common stock sold to related parties	March 2018 Public Offering Number of Aggregate Shares of Purchase Common Stock Price Owners of More Than 5% of Our Common Stock FMR LLC 1,176,470 $ 9,999,995 OrbiMed Advisors LLC (1) 588,235 4,999,998 Novo Holdings A/S (2) 1,176,470 9,999,995 Adams Street Partners (3) 588,235 4,999,998 Board of Directors Richard A. Miller, M.D. 100,000 850,000 (1) Peter Thompson, M.D., a member of our Board of Directors since November 2014, is a Private Equity Partner at OrbiMed Advisors, LLC. (2) Peter Moldt, Ph.D., a Partner at Novo Ventures (US) Inc., which provide certain consultancy services to Novo Holdings A/S, served as a member of our Board of Directors from January 2015 to January 2019. (3) Elisha P. (Terry) Gould III, a member of our Board of Directors since November 2014, is a Partner at Adams Street Partners, LLC.

Quarterly Selected Financial _2

Quarterly Selected Financial Data (unaudited) (Tables)	12 Months Ended
	Dec. 31, 2019
Quarterly Selected Financial Data (unaudited)
Quarterly Selected Financial Data (unaudited)	Quarter Ended December 31, September 30, June 30, March 31, (in thousands, except per share amounts) 2019 2019 2019 2019 Operating expenses $ 11,440 $ 11,513 $ 13,596 $ 12,305 Net loss (11,047) (11,004) (12,978) (11,643) Net loss per share, basic and diluted $ (0.38) $ (0.37) $ (0.44) $ (0.40) Quarter Ended December 31, September 30, June 30, March 31, (in thousands, except per share amounts) 2018 2018 2018 2018 Operating expenses $ 11,171 $ 11,149 $ 12,258 $ 14,644 Net loss (10,509) (10,498) (11,631) (14,301) Net loss per share, basic and diluted $ (0.36) $ (0.36) $ (0.40) $ (0.63)

Organization - Public Offerings

Organization - Public Offerings (Details) - USD ($) $ / shares in Units, $ in Thousands	Nov. 08, 2019	Apr. 26, 2016	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Public Offerings
Proceeds from sale of stock					$ 64,877	$ 711
Accumulated deficit				$ (217,145)	$ (170,473)
Cash, cash equivalents and short-term marketable securities				$ 78,000
Common stock, par value (in dollars per share)				$ 0.0001	$ 0.0001
Exchange Warrants
Public Offerings
Issuance of stock (in shares)	1,458,000			1,458,000
Common stock, par value (in dollars per share)	$ 0.0001
Exchange warrants issued	1,458,000
Warrant exercise price	$ 0.0001
Exchange warrant expiry term	10 years
Percentage of shares owned by exchanging shareholders	9.99%
Warrants Exercised				0
Over-Allotment Option
Public Offerings
Shares Issued, Price Per Share		$ 15
Issuance of stock (in shares)		502,618	1,058,823
Follow On Public Offering
Public Offerings
Shares Issued, Price Per Share			$ 8.50
Proceeds from sale of stock			$ 64,900
Issuance of stock (in shares)			8,117,647

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Basis of Presentation, Credit Risk and Income Taxes (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)segmentitem	Jan. 01, 2019USD ($)	Dec. 31, 2018USD ($)
Accumulated deficit	$ (217,145)		$ (170,473)
Cash, cash equivalents and marketable securities	$ 78,000
Concentrations of Credit Risk and Other Risks and Uncertainties
Number of financial institutions used for cash and cash equivalent deposits | item	2
Segments
Number of operating segments | segment	1
Recent accounting pronouncements
Operating lease right-of-use asset	$ 2,327		$ 0
Operating lease liabilities	$ 3,188
ASU 2016-02
Recent accounting pronouncements
Operating lease right-of-use asset		$ 2,800
Operating lease liabilities		3,800
Deferred rent		$ 1,000

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Property and Equipment, Net (Details)	12 Months Ended
	Dec. 31, 2019
Laboratory equipment
Property and Equipment, Net
Estimated Useful lives	5 years
Computer equipment and purchased software
Property and Equipment, Net
Estimated Useful lives	3 years

Net Loss per Share - Net Loss p

Net Loss per Share - Net Loss per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Numerator:
Net loss - basic and diluted	$ (11,047)	$ (11,004)	$ (12,978)	$ (11,643)	$ (10,509)	$ (10,498)	$ (11,631)	$ (14,301)	$ (46,672)	$ (46,939)	$ (55,663)
Denominator:
Weighted average common shares outstanding									29,364,535	27,686,909	20,958,557
Less: weighted average common shares subject to repurchase									(14,725)	(176,949)	(470,051)
Weighted average common shares outstanding used to compute basic and diluted net loss per share									29,349,810	27,509,960	20,488,506
Net loss per share, basic and diluted (in dollars per share)	$ (0.38)	$ (0.37)	$ (0.44)	$ (0.40)	$ (0.36)	$ (0.36)	$ (0.40)	$ (0.63)	$ (1.59)	$ (1.71)	$ (2.72)

Net Loss per Share - Anti-Dilut

Net Loss per Share - Anti-Dilutive Securities (Details) - shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Excluded from the calculation of diluted net loss per share, due to anti-dilutive effect
Shares of common stock equivalents	5,643,410	3,821,335	3,332,597
Common stock subject to repurchase
Excluded from the calculation of diluted net loss per share, due to anti-dilutive effect
Shares of common stock equivalents		43,076	319,203
Outstanding options
Excluded from the calculation of diluted net loss per share, due to anti-dilutive effect
Shares of common stock equivalents	5,643,410	3,778,259	3,013,394

Fair Value Measurements - Recur

Fair Value Measurements - Recurring (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Transfer between levels
Transfer of assets from level 1 to 2	$ 0	$ 0
Transfer of assets from level 2 to 1	0	0
Transfer of liabilities from level 1 to 2	0	0
Transfer of liabilities from level 2 to 1	0	0
Transfer of assets into level 3	0	0
Transfer of assets out of level 3	0	0
Transfer of liabilities into level 3	0	0
Transfer of liabilities out of level 3	$ 0	0
Assets
Maximum remaining maturity of marketable securities	10 months
Recurring
Assets
Cash equivalents	$ 4,252	38,698
Marketable securities	72,828	75,401
Total Assets	77,080	114,099
Recurring | Level 1
Assets
Cash equivalents	4,252	38,698
Marketable securities	7,023
Total Assets	11,275	38,698
Recurring | Level 2
Assets
Marketable securities	65,805	75,401
Total Assets	$ 65,805	$ 75,401

Fair Value Measurements - Avail

Fair Value Measurements - Available For Sale (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Fair value of available for sale marketable securities
Amortized Cost	$ 72,799	$ 75,435
Gross Unrealized Gains	37
Gross Unrealized Losses	(8)	(34)
Fair Value	72,828	75,401
U.S. Treasury securities
Fair value of available for sale marketable securities
Amortized Cost	7,019
Gross Unrealized Gains	4
Fair Value	7,023
U.S. Government agency securities
Fair value of available for sale marketable securities
Amortized Cost	17,701	49,124
Gross Unrealized Gains	16
Gross Unrealized Losses		(27)
Fair Value	17,717	49,097
Corporate debt obligations
Fair value of available for sale marketable securities
Amortized Cost	48,079	26,311
Gross Unrealized Gains	17
Gross Unrealized Losses	(8)	(7)
Fair Value	$ 48,088	$ 26,304

License and Collaboration Agr_2

License and Collaboration Agreements (Details) - USD ($)	1 Months Ended	12 Months Ended
	Feb. 28, 2015	Dec. 31, 2019	Dec. 31, 2015	Feb. 28, 2017
Monash License
License and Collaboration Agreements
Minimum annual fee		$ 25,000
Aggregate potential milestone payments		$ 45,100,000
Period of written notice to terminate		30 days
Monash License | Research and development
License and Collaboration Agreements
One-time cash payment		$ 275,000
Licensing Agreement | Scripps Research Institute
License and Collaboration Agreements
Minimum annual fee			$ 25,000
Aggregate potential milestone payments			$ 2,600,000
Milestone payments made		$ 0
Period of written notice to terminate			90 days
Licensing Agreement | Scripps Research Institute | Research and development
License and Collaboration Agreements
One-time cash payment			$ 10,000
Licensing Agreement | Vernalis (R&D) Limited
License and Collaboration Agreements
Milestone payments made				$ 3,000,000
Period of written notice to terminate	90 days
Licensing Agreement | Vernalis (R&D) Limited | Minimum
License and Collaboration Agreements
Aggregate potential milestone payments	$ 220,000,000
Licensing Agreement | Vernalis (R&D) Limited | Research and development
License and Collaboration Agreements
One-time cash payment	$ 1,000,000

Balance Sheet Components - Prep

Balance Sheet Components - Prepaid and Other Current Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Prepaid and Other Current Assets
Interest receivable	$ 329	$ 337
Prepaid research and development manufacturing expenses	240	75
Prepaid facility expenses	157	149
Prepaid insurance	150	166
Other	486	265
Total of prepaid and other current assets	$ 1,362	$ 992

Balance Sheet Components - Prop

Balance Sheet Components - Property and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Property and Equipment
Property and equipment, gross	$ 4,622	$ 4,597
Less: accumulated depreciation and amortization	(3,160)	(2,417)
Property and equipment, net	1,462	2,180
Laboratory equipment
Property and Equipment
Property and equipment, gross	2,396	2,371
Computer equipment and purchased software
Property and Equipment
Property and equipment, gross	142	142
Leasehold improvements
Property and Equipment
Property and equipment, gross	$ 2,084	$ 2,084

Balance Sheet Components - Accr

Balance Sheet Components - Accrued and Other Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Accrued and Other Liabilities
Accrued clinical trial related	$ 4,300	$ 2,718
Accrued manufacturing expense	696	1,077
Personnel related	1,624	649
Other accrued expenses	279	585
Total of accrued and other liabilities	$ 6,899	$ 5,029

Balance Sheet Components - Othe

Balance Sheet Components - Other Liabilities (Details) $ in Thousands	Dec. 31, 2018USD ($)
Other Liabilities
Deferred rent	$ 869
Total of other liabilities	$ 869

Common Stock (Details)

Common Stock (Details)	Nov. 08, 2019shares	Dec. 31, 2019USD ($)Voteshares	Dec. 31, 2018USD ($)shares	Dec. 31, 2017USD ($)shares
Common Stock
Common stock, shares authorized for issuance		290,000,000	290,000,000
Preferred stock, shares authorized for issuance		10,000,000	10,000,000
Number of votes per share of common stock | Vote		1
Dividends on common stock | $		$ 0
Proceeds from sale of stock | $			$ 64,877,000	$ 711,000
Shares of common stock reserved for issuance, on an as-converted basis
Shares available for future option grants		1,704,183	2,486,637	2,576,535
Outstanding options		5,643,410	3,778,259	3,013,394
Unvested restricted common stock (founders and early exercise of stock options)			43,076	319,203
Shares reserved for employee stock purchase plan		400,000	400,000	400,000
Total		9,205,593	6,707,972	6,309,132
Exchange Warrants
Shares of common stock reserved for issuance, on an as-converted basis
Exchange warrants	1,458,000	1,458,000

Stock Option Plans - Stock Opti

Stock Option Plans - Stock Option Activity (Details) $ / shares in Units, $ in Thousands	1 Months Ended		12 Months Ended
	Mar. 31, 2016itemshares	Feb. 28, 2014	Dec. 31, 2019USD ($)$ / sharesshares	Dec. 31, 2018USD ($)$ / sharesshares	Dec. 31, 2017USD ($)shares
Shares Available for Grant
Beginning balance			2,486,637	2,576,535
Exercised | $			$ 24	$ 393	$ 731
Ending balance			1,704,183	2,486,637	2,576,535
Number of Options
Beginning balance			3,778,259	3,013,394
Ending balance			5,643,410	3,778,259	3,013,394
2014 Plan
Stock Option Plans
Vesting period		4 years
Maximum exercise term		10 years
Exercise price of common stock of its fair value (as a percent)		100.00%
Number of awards to be granted in future | item	0
Maximum number of options that may be re-issued under the 2016 plan	1,136,229
2016 Plan
Stock Option Plans
Vesting period	4 years
Maximum exercise term	10 years
Exercise price of common stock of its fair value (as a percent)	100.00%
Shares Available for Grant
Beginning balance			2,486,637
Additional shares authorized			1,170,000
Granted			(2,029,000)
Forfeited			76,546
Ending balance			1,704,183	2,486,637
Number of Options
Beginning balance			3,778,259
Granted			2,029,000
Exercised				(87,303)
Forfeited			(76,546)
Ending balance			5,643,410	3,778,259
Weighted-Average Exercise Price
Beginning balance (in dollars per share) | $ / shares			$ 10.32
Granted (in dollars per share) | $ / shares			3.61
Exercised (in dollars per share) | $ / shares				$ 0.28
Forfeited (in dollars per share) | $ / shares			11.67
Ending balance (in dollars per share) | $ / shares			$ 8.05	$ 10.32

Stock Option Plan - Exercise Pr

Stock Option Plan - Exercise Price Range (Details) - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Information about stock options outstanding
Options Outstanding, Number	5,643,410	3,778,259
Options Outstanding, Weighted Average Remaining Contractual Life	8 years 4 months 17 days	8 years 6 months 7 days
Weighted average exercise price of options outstanding (in dollars per share)	$ 8.05	$ 10.32
Options Vested, Number	2,210,969	1,369,145
Options Vested, Weighted Average Remaining Contractual Life	7 years 18 days	7 years 5 months 16 days
Weighted average exercise price of options vested (in dollars per share)	$ 11.66	$ 11.60
Weighted average grant date fair value of options granted (in dollars per share)	2.53	5.23	$ 8.93
$0.28 - $2.56
Information about stock options outstanding
Exercise Price, low end of range (in dollars per share)	0.28
Exercise Price, high end of range (in dollars per share)	$ 2.56
Options Outstanding, Number	191,000
Options Outstanding, Weighted Average Remaining Contractual Life	5 years 7 months 28 days
Weighted average exercise price of options outstanding (in dollars per share)	$ 0.36
Options Vested, Number	184,730
Options Vested, Weighted Average Remaining Contractual Life	5 years 6 months 7 days
Weighted average exercise price of options vested (in dollars per share)	$ 0.29
$3.01 - $4.65
Information about stock options outstanding
Exercise Price, low end of range (in dollars per share)	3.01
Exercise Price, high end of range (in dollars per share)	$ 4.65
Options Outstanding, Number	2,027,500
Options Outstanding, Weighted Average Remaining Contractual Life	9 years 9 months
Weighted average exercise price of options outstanding (in dollars per share)	$ 3.61
Options Vested, Number	32,375
Options Vested, Weighted Average Remaining Contractual Life	6 years 4 days
Weighted average exercise price of options vested (in dollars per share)	$ 4.64
$4.84 - $7.59
Information about stock options outstanding
Exercise Price, low end of range (in dollars per share)	4.84
Exercise Price, high end of range (in dollars per share)	$ 7.59
Options Outstanding, Number	1,061,522
Options Outstanding, Weighted Average Remaining Contractual Life	8 years 11 months 9 days
Weighted average exercise price of options outstanding (in dollars per share)	$ 5.95
Options Vested, Number	261,504
Options Vested, Weighted Average Remaining Contractual Life	8 years 10 months 24 days
Weighted average exercise price of options vested (in dollars per share)	$ 5.98
$9.52 - $14.43
Information about stock options outstanding
Exercise Price, low end of range (in dollars per share)	9.52
Exercise Price, high end of range (in dollars per share)	$ 14.43
Options Outstanding, Number	1,051,738
Options Outstanding, Weighted Average Remaining Contractual Life	7 years 11 months 23 days
Weighted average exercise price of options outstanding (in dollars per share)	$ 10.83
Options Vested, Number	593,596
Options Vested, Weighted Average Remaining Contractual Life	7 years 11 months 5 days
Weighted average exercise price of options vested (in dollars per share)	$ 10.90
$15.00 - $16.70
Information about stock options outstanding
Exercise Price, low end of range (in dollars per share)	15	15
Exercise Price, high end of range (in dollars per share)	$ 16.70	$ 16.70
Options Outstanding, Number	1,311,650	1,348,526
Options Outstanding, Weighted Average Remaining Contractual Life	6 years 6 months 4 days	7 years 6 months
Weighted average exercise price of options outstanding (in dollars per share)	$ 15.49	$ 15.49
Options Vested, Number	1,138,764	834,456
Options Vested, Weighted Average Remaining Contractual Life	6 years 5 months 9 days	7 years 4 months 17 days
Weighted average exercise price of options vested (in dollars per share)	$ 15.40	$ 15.37
$0.28 - $4.65
Information about stock options outstanding
Exercise Price, low end of range (in dollars per share)		0.28
Exercise Price, high end of range (in dollars per share)		$ 4.65
Options Outstanding, Number		301,803
Options Outstanding, Weighted Average Remaining Contractual Life		6 years 5 months 9 days
Weighted average exercise price of options outstanding (in dollars per share)		$ 0.72
Options Vested, Number		261,373
Options Vested, Weighted Average Remaining Contractual Life		6 years 5 months 1 day
Weighted average exercise price of options vested (in dollars per share)		$ 0.68
$5.94 - $9.52
Information about stock options outstanding
Exercise Price, low end of range (in dollars per share)		5.94
Exercise Price, high end of range (in dollars per share)		$ 9.52
Options Outstanding, Number		1,101,750
Options Outstanding, Weighted Average Remaining Contractual Life		9 years 11 months 1 day
Weighted average exercise price of options outstanding (in dollars per share)		$ 6.10
Options Vested, Number		3,585
Options Vested, Weighted Average Remaining Contractual Life		8 years 8 months 9 days
Weighted average exercise price of options vested (in dollars per share)		$ 8.92
$9.60 - $14.43
Information about stock options outstanding
Exercise Price, low end of range (in dollars per share)		9.60
Exercise Price, high end of range (in dollars per share)		$ 14.43
Options Outstanding, Number		1,026,180
Options Outstanding, Weighted Average Remaining Contractual Life		8 years 11 months 19 days
Weighted average exercise price of options outstanding (in dollars per share)		$ 10.89
Options Vested, Number		269,731
Options Vested, Weighted Average Remaining Contractual Life		8 years 8 months 12 days
Weighted average exercise price of options vested (in dollars per share)		$ 10.56

Stock Option Plan - Vested or E

Stock Option Plan - Vested or Expected to Vest (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Options outstanding and exercisable
Vested, Number of Shares (in shares)	2,210,969
Vested, Weighted Average Exercise Price (in dollars per share)	$ 11.66
Vested, Weighted Average Remaining Contractual Life	7 years 18 days
Vested, Aggregate Intrinsic Value	$ 977,587
Expected to vest, Number of Shares (in shares)	3,432,441
Expected to vest, Weighted Average Exercise Price (in dollars per share)	$ 5.72
Expected to vest, Weighted Average Remaining Contractual Life	9 years 2 months 27 days
Expected to vest, Aggregate Intrinsic Value	$ 3,713,778
Fair value of common stock (in dollars per share)	$ 5.44
Aggregate intrinsic value of stock options exercised	$ 400	$ 1,100	$ 300
Fair value of options vested	$ 7,800	$ 7,100	$ 5,800

Stock-Based Compensation - Expe

Stock-Based Compensation - Expense Allocation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Stock-based compensation
Stock-based compensation expense	$ 7,348	$ 7,135	$ 6,229
Research and development
Stock-based compensation
Stock-based compensation expense	3,103	2,919	2,692
General and administrative
Stock-based compensation
Stock-based compensation expense	$ 4,245	$ 4,216	$ 3,537

Stock Based Compensation -Valua

Stock Based Compensation -Valuation Assumptions Employees (Details) - Employee stock options - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Weighted-average assumptions used to estimate fair value of share-based awards
Risk-free interest rate	1.90%	2.80%	2.10%
Expected volatility	82.10%	82.70%	91.40%
Expected term (in years)	6 years	6 years	6 years
Expected dividend yield	0.00%	0.00%	0.00%
Unrecognized compensation expense	$ 13.4	$ 15.8	$ 18.6
Expected period for recognizing compensation expense	2 years 8 months 16 days	2 years 8 months 19 days	2 years 10 months 6 days

Income Taxes - Components of lo

Income Taxes - Components of loss before income tax and Income tax benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Taxes
Income tax benefits	$ 0	$ 0	$ 0
Components of loss before income tax
Domestic	(46,672)	(47,096)	(28,253)
Foreign		157	(27,410)
Total	$ (46,672)	$ (46,939)	$ (55,663)

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of effective tax rate (Details)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reconciliation of the effective tax rate to the U.S. Federal statutory rate
Federal tax benefit at statutory rate	21.00%	21.00%	34.00%
State tax, net of Federal benefit	6.00%	9.00%	7.00%
Foreign rate differential			(17.00%)
Federal rate change impact			(9.00%)
Change in valuation allowance	(28.00%)	(41.00%)	(16.00%)
Research and development tax credits	3.00%	2.00%	2.00%
Prior year federal true-up		10.00%	(3.00%)
Other	(2.00%)	(1.00%)	2.00%
Effective income tax rate	0.00%	0.00%	0.00%

Income Taxes - Deferred tax ass

Income Taxes - Deferred tax assets net (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Net operating loss carryforwards	$ 42,486	$ 31,533	$ 15,438
Tax credit carryforwards	6,990	6,441	4,351
Capitalized tax assets		138	131
Capitalized tax assets	(3)
Accruals	152	188	183
Stock compensation	4,317	2,879	1,730
Operating lease liability	892
Other	40	58	52
Total deferred tax assets	54,874	41,237	21,885
Deferred tax liabilities
Operating lease right-of-use asset	(651)
Valuation allowance	(54,223)	(41,237)	(21,885)
Net deferred tax assets	0	0	$ 0
Increase in valuation allowance	$ 13,000	$ 19,400

Income Taxes - Operating loss c

Income Taxes - Operating loss carryforwards (Details) $ in Millions	Dec. 31, 2019USD ($)
Federal
Net operating loss carryforwards
NOL carryforwards	$ 144.5
State
Net operating loss carryforwards
NOL carryforwards	$ 173.9

Income Taxes - Tax credit carry

Income Taxes - Tax credit carry forwards (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Tax credit carryforwards
Common stock, shares issued	27,953,233	29,323,930
Research and development credits | Federal
Tax credit carryforwards
Research and development tax credit carryforwards	$ 6.1
Research and development credits | State
Tax credit carryforwards
Research and development tax credit carryforwards	$ 3.3

Income Taxes - Unrecognized tax

Income Taxes - Unrecognized tax benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Summary of unrecognized tax benefits
Unrecognized tax benefits beginning of the period	$ 1,804	$ 1,219	$ 604
Decrease related to the prior year	(365)		(51)
Increased related to the current year	446	585	666
Unrecognized tax benefits, end of the period	1,885	1,804	1,219
Income tax - accrual for interest or penalties	$ 0	$ 0	$ 0

Facility Lease - Lessee informa

Facility Lease - Lessee information (Details) $ in Thousands	46 Months Ended
	Oct. 31, 2018USD ($)ft²	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Jan. 31, 2015ft²
Lessee Disclosure [Abstract]
Area of leased facility | ft²	27,280			8,138
Lease term				1 year
Landlord Provided Free Rent And Lease Incentives	$ 1,900
Operating lease right-of-use asset		$ 2,327	$ 0

Facility Lease - Lease cost (De

Facility Lease - Lease cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating lease cost
Operating lease costs	$ 960	$ 748	$ 734
Costs of non-lease components (previously common area maintenance)	324	296	281
Total operating lease cost	1,284	1,044	1,015
Other Information
Operating cash flows used for operating lease	$ 1,449	$ 1,389	$ 1,398
Remaining lease term	3 years 1 month 6 days	4 years 1 month 6 days	3 years 1 month 6 days
Discount rate	10.00%

Facility Lease - Minimum rental

Facility Lease - Minimum rental commitments (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Minimum rental commitments under Topic 842
2020	$ 1,159
2021	1,260
2022	1,299
Total lease payments	3,718
Less: imputed interest	(530)
Total	$ 3,188
Minimum rental commitments under Topic 840
2019		$ 1,110
2020		1,142
2021		1,251
2022		1,296
2023		109
Total		$ 4,908

Commitments and Contingencies -

Commitments and Contingencies - Line of Credit (Details) $ in Millions	Aug. 31, 2015USD ($)
Line of credit
Security deposit	$ 0.1
Secured debt
Line of credit
Line of credit	$ 0.1

Related Party Transaction (Deta

Related Party Transaction (Details) - USD ($)	Apr. 26, 2016	Mar. 29, 2016	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
Public Offerings
Proceeds from sale of stock				$ 64,877,000	$ 711,000
Director
Related Party Transaction
Purchase of research services					$ 461,000
IPO
Public Offerings
Share offering price		$ 15
Exchange warrants		4,700,000
Net proceeds from IPO	$ 70,600,000
Over-Allotment Option
Public Offerings
Share offering price	$ 15
Exchange warrants	502,618		1,058,823
Follow On Public Offering
Public Offerings
Share offering price			$ 8.50
Exchange warrants			8,117,647
Proceeds from sale of stock			$ 64,900,000
Follow On Public Offering | FMR LLC
Public Offerings
Exchange warrants			1,176,470
Owners of More Than 5% of Our Common Stock or Board of Directors
Aggregate Purchase Price			$ 9,999,995
Follow On Public Offering | Orbimed Advisors LLC
Public Offerings
Exchange warrants			588,235
Owners of More Than 5% of Our Common Stock or Board of Directors
Aggregate Purchase Price			$ 4,999,998
Follow On Public Offering | Novo Holdings A/S
Public Offerings
Exchange warrants			1,176,470
Owners of More Than 5% of Our Common Stock or Board of Directors
Aggregate Purchase Price			$ 9,999,995
Follow On Public Offering | Adams Street Partners
Public Offerings
Exchange warrants			588,235
Owners of More Than 5% of Our Common Stock or Board of Directors
Aggregate Purchase Price			$ 4,999,998
Follow On Public Offering | Director
Public Offerings
Exchange warrants			100,000
Owners of More Than 5% of Our Common Stock or Board of Directors
Aggregate Purchase Price			$ 850,000

Quarterly Selected Financial _3

Quarterly Selected Financial Data (unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly Selected Financial Data (unaudited)
Operating Expenses	$ 11,440	$ 11,513	$ 13,596	$ 12,305	$ 11,171	$ 11,149	$ 12,258	$ 14,644	$ 48,854	$ 49,222	$ 56,524
Net loss	$ (11,047)	$ (11,004)	$ (12,978)	$ (11,643)	$ (10,509)	$ (10,498)	$ (11,631)	$ (14,301)	$ (46,672)	$ (46,939)	$ (55,663)
Net loss per share, basic and diluted (in dollars per share)	$ (0.38)	$ (0.37)	$ (0.44)	$ (0.40)	$ (0.36)	$ (0.36)	$ (0.40)	$ (0.63)	$ (1.59)	$ (1.71)	$ (2.72)